POLYMER BLENDS AND PROCESSING PROGRAM

Applications of polymer blends and multiphase polymer materials continue to enjoy growth in terms of market share, consumption, and employment within the plastics industry. This growth challenges the flexibility of materials suppliers to meet customer needs with new materials and reduced product development cycles. The futility of trial and error approaches to address these challenges led industry to solicit measurement tools and methods of analysis which enhance their efforts to understand and control resin compatibility, phase morphology, and material properties. These demands are further sharpened by the advent of methods that provide better control in polymer synthesis, more precise molecular structure, and new nanoscale material components.

The Polymer Blends and Processing Program began with clear scientific goals to establish expertise in static and kinetic aspects of phase behavior in polymer blends, effects of shear flow on mixing and separating, and reactive processing to promote compatibility. The focus on these areas furthers program objectives by accelerating development of new measurement tools, including specialized light and neutron scattering methods, and by applying those tools to expand the knowledge base for thermodynamics and kinetics of polymer blends. Work extends to the effects of additives in a blend system, the relative behavior of blends in bulk compared to that in thin films at interfaces, and the effects of complex thermal and mechanical histories on the phase separation process. Fundamental advances in theory and modeling in collaboration with CTCMS continue to guide and interpret these measurements.

Current research in the program has four areas of emphasis: (1) measurement technology for on-line characterization of phase behavior, deformation, and dispersion; (2) shear effects on phase diagrams and blend morphology; (3) interfacial interactions in compatibilized blends, filled polymers, and nanocomposites; and (4) control thin films morphology by surface interactions and finite size effects. Active industrial collaborators include: Dow Chemical, Dow Corning, Eastman Chemical, Exxon, GE, Goodyear, Lucent Technologies, Mobil, ChemElectroPhys, Packard Electric, Dendritech, and DSM for development of measurements using fluorescence, light scattering, neutron scattering and reflectivity, x-ray scattering, birefringence, microscopy (AFM, TEM, phase contrast), and rheology.

In fiscal year 1998 special emphasis was put on developing the programs in polymer fillers and nanocomposites and applications of dendritic polymers. Two NIST/Industry workshops were held to identify and prioritize the critical technical issues hindering new applications in these two areas. For fillers and nanocomposites a number of important needs were identified with the conclusion that the most critical were controlling molecular level interactions and measuring dynamics of polymers at the filler interface. For dendritic polymers important issues included direct comparisons of structures of dendritic polymers, characterization of interactions with other polymers, and, most critically, properties of dendritic polymers at interfaces. The workshops also provided an opportunity to communicate the cutting edge work of the blends and processing program.

Significant Accomplishments

• The versatility of hydrogen-bonded polymer blends for advanced materials was demonstrated and a new phenomenological model for the strength of the bonding interaction was tested and confirmed by small angle neutron scattering.
• A model based on normal stress differences was developed which predicts the onset of highly anisotropic structures in the vorticity direction for phase separated blends under shear when the droplet first normal stress difference exceeds that of the matrix.
• An optical sensor to measure anisotropy during biaxial stretching of polypropylene film in production ovens at high temperature was designed and demonstrated in collaboration with Mobil Chemical Company.
• Spherical and cylindrical composition waves emanating from the boundaries of inclusions in a phase separating blend were predicted by simulations and subsequently confirmed by experiments investigating the microstructure of filled model polymer blends.
• An analytical model predicting the viscosity for polymers filled with dispersions of platelet particles was developed and validated with data for a range of particle shapes. The threshold of rigidity where the suspension viscosity diverges was predicted to be inversely proportional to the intrinsic viscosity.
• Modeling of finite size effects agrees with measurements by showing that surface confinement can shift phase boundaries in compressible blends up or down depending on the strength of polymer-surface interactions.
• Theoretical concepts and simulations were developed to describe the growth of dynamical correlations that are related to slow dynamics in glass forming materials.
• X-ray reflectivity and atomic force microscopy methods were developed to characterize interactions between clay and polymer in nanocomposite films under well defined conditions.
• Alignment of the morphology in a phase separating blend film to an underlying pattern of surface chemisty was shown to improve with decreasing film thickness until reaching a critical value below which spinodal dewetting causes controlled break-up into uniform nanoscale droplets.
• Interpenetrating polymer networks of hydroxyethylmethacrylate with polyamidoamine (PAMAM) dendrimers were prepared and the individual dendrimers were shown by small angle x-ray scattering and transmission electron microscopy to be uniformly dispersed.
• Thorough characterization of the size, shape, and molecular conformation of PAMAM dendrimer molecules of generations 5 through 10 was achieved with a combination of small angle neutron and x-ray scattering and transmission electron microscopy.
• The single chain dimensions of polyelectrolytes as measured by zero-average-contrast small angle neutron scattering, were shown to be consistent with semiflexible rods in the presence of monovalent counterions and random coils in the presence of divalent counterions.

Phase Behavior in Polymer Blends

C. C. Han, H. Gruell¹, A. Esker², R. Xie², A. I. Nakatani, C. L. Jackson, A. Karim, and G. Kim^3
1Alexander von Humboldt Foundation, Germany
²University of Connecticut, Storrs, Connecticut
³Stevens Institute of Technology, Hoboken, New Jersey

Objectives
The objectives are to develop experimental techniques and capabilities for studying morphologies of polymer blends resulting from phase separation and crystallization both at surfaces and in the bulk in order to understand the mechanisms by which these processes occur. Of particular interest are questions about: the interplay between crystallization and phase separation in blends and in microphase separated copolymers where both processes are present; the role strong and steric interactions have on the stabilization of phase separated morphologies; finite size effects, which influence and control film stability and polymer miscibility in nanotechnology applications; the role of the preferential interaction of polymer components with a surface and the growth of adsorbed layers (pre-transition) and subsequent phase separation; and finally, the effect semi-permeable, ultra-thin, barrier layers (membranes) have on selective polymer transport process.

Technical Description
Small angle neutron scattering (SANS), light scattering (LS), optical microscopy (OM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and reflectivity (x-ray (XR) and neutron (NR)) are being used and modified to examine the time dependent evolution of morphologies associated with preferential adsorption, wetting/dewetting, mixing/demixing and crystallization in polymer blends at surfaces, in confined geometries and in the bulk.

• AFM capabilities will be developed to probe the role surface interactions have on polymer film stability (wetting/dewetting) with homopolymers for subsequent blend studies of these phenomena.
• Polystyrene/polybutadiene and polybutadiene/polyisoprene on flat silicon surfaces are being studied by NR and SANS and followed by a bulk system with fine silica particles.
• The phase behavior of polymer blends stabilized by H-bonding and metal ion complexes have been studied by SANS.
• The effect of conformational changes on steric interactions induced through photoisomerization has been examined by SANS.
• Blends of polystyrene and polycaprolactone which have an upper critical solution temperature will be examined as to the interplay of crystallization and phase separation on both the kinetics of phase separation and the ultimate morphologies, at appropriate relative quench depths by LS and microscopy.
• Microphase separation and crystallization in semi-crystalline block copolymers of polystyrene(S)-polybutadiene(B)-polycaprolactone(C) and diblocks SC and BC will be studied using optical microscopy (OM), transmission electron microscopy (TEM) and scattering techniques.
• Alkyl branch modification of stiff rods (thereby forming "hairy-rods") in bulk and on a surface are being studied by the aforementioned techniques.
• Trilayer thin films of spin-coated deuterated polystyrene, membranes prepared by the Langmuir-Blodgett technique, and hydrogenated polystyrene will be prepared and characterized where the membrane consists of a blend of photo-crosslinkable cellulose "hairy-rods" and polystyrene. NR provides a convenient way to study the diffusion of this system, while characterization of the membrane and layer thicknesses are readily obtained from the other techniques.

External Collaborators
A. Halasa, Y. Feng, Goodyear Tire and Rubber Company, Akron, Ohio - Collaboration and supply of elastomers and filled elastomers for various experiments.

R. A. Weiss, University of Connecticut, Storrs, Connecticut - Collaboration and supply of ionomer blend materials.

R. Stadler, University of Bayreuth, Bayreuth, Germany - Collaboration and supply of polycaprolactone (PCL) and PCL block copolymer.

T. Hashimoto, H. Jinnai, ERATO, Japan Science and Technology Corporation, Kyoto, Japan

O. Urakawa, Q. Tran-Cong, Kyoto Institute of Technology, Kyoto, Japan - Collaboration and supply of materials for SANS experiments on the effect of photoisomerization in polymer blends.

M. Libera, Stevens Institute of Technology, Hoboken, New Jersey - Collaboration on TEM of block copolymers.

G. Wegner, Max-Planck-Institut für Polymerforschung, Mainz, Germany

Accomplishments

• The role of capillary waves on film breakup was investigated and a conceptual model was introduced involving three film thickness regimes defined in terms of the amplitude of capillary waves relative to the film thickness. The "spinodal dewetting" mechanism characterizing the ultrathin film regime was observed by AFM.
• The bulk phase behavior of a polyisoprene/deuterated polybutadiene blend was determined by SANS measurements. The system shows lower critical solution temperature (LCST) behavior with a bulk critical temperature of 55 °C and a critical composition of f_dPB = 0.45 (where f_dPB is the volume fraction of deuterated polybutadiene). The phase behavior of this blend in a thin film geometry was investigated by multiple neutron reflection experiments as a function of temperature (298 K< T < 408 K) and film thickness (400 Å < d< 2000 Å). The depth profile shows a preferential symmetric adsorption of polyisoprene at both interfaces consistent with Monte Carlo simulation studies. The surface excess, z*, of polyisoprene as a function of temperature shows a maximum around the bulk critical temperature and linearly increases with the logarithm of film thickness for a given temperature. The results suggest that in the one phase region adsorption layers of polyisoprene are formed which grow in size with increasing film thickness and as the critical temperature is approached. In the two-phase region, phase separation occurs inside the film with the polyisoprene rich phase wetting both interfaces. For thick films, a trilayer structure is formed with the polybutadiene rich phase in the center of the film and the polyisoprene rich phase wetting both interfaces (polymer/air and polymer/Si). This structure becomes more and more unstable with decreasing film thickness leading to lateral inhomogeneities inside the film.
• A phenomenological model was formulated for how the strength of the binding interaction in hydrogen-bonded polymer blends depends on the density of the hydroxyl group. This model was tested by SANS in order to deduce the hydrogen bond enthalpy. The demonstrated complexity of the low-q structure in these materials was linked to the equilibrium properties of the condensed phase. The use and versatility of this type of chemical modification technique for enhancing polymer-polymer miscibility for advanced materials processing was also demonstrated.
• Control over the miscibility of polymer blends by manipulating steric interactions through controlled photoisomerization of labeled polymer chains was demonstrated by SANS measurements.
• A model blend system of polystyrene and polycaprolactone was purified and cloud point experiments planned to study the competition between crystallization and phase separation. Necessary modifications have been initiated for the existing temperature jump light scattering instrument to study phase separation kinetics and subsequently probe crystallization kinetics following a second temperature quench.
• TEM was used to study thick films (5-10 µm) and bulk specimens of polystyrene(S)-polybutadiene(B)-polycaprolactone(C) (SBC) triblock and BC diblock copolymers prepared by various annealing conditions, with or without spherulitic crystalline morphology. A comparison of the macroscopic crystalline superstructure (optical range 4-1000 µm) and microphase separated morphology (TEM range 5-100 nm) showed that crystallization into spherulites can either distort or completely destroy the microphase-separated morphology. In the SBC triblock, long range crystallization of the C block can be suppressed by appropriate annealing conditions, as seen by TEM and OM. In this case, the microphase-separated structure resembles that seen for ABC type amorphous block copolymers; for S₃₅B₁₅C₅₀ a lamellar microstructure with B cylinders at the interphase boundaries is observed. The competition between microphase separation and crystallization of the C block depends strongly on the rubbery or glassy character of the amorphous blocks and the overall composition. SC diblock copolymers form a lamellar microphase separated structure which is prevented from spherulitic crystallization due to the glassy S blocks at 62 mass %.
• Langmuir-Blodgett thin film blends of cellulose ethers with polystyrene were characterized by XR and AFM for use as membrane materials. Crystallization conditions were determined for bulk blends of cellulose ethers and esters with polycaprolactone and poly(ethylene oxide) for use as model systems for studying crystallization kinetics by LS where the rigidity of the cellulose backbone may induce substantial changes in morphology.
• NR measurements were performed to characterize the interdiffusion of deuterated and protonated polystyrene in the presence and absence of a membrane. The porosity of the membrane can be controlled by mixing 0 to 40 % polystyrene into the cellulose ether to form a phase separated structure. The membrane thickness can be varied in increments of 10 Å corresponding to the thickness of a single monolayer. The presence of a 60 Å thick membrane containing 34% PS substantially retards interdiffusion. Movement of the membrane as a function of annealing time is observed and may be represent a polymeric analog to similar observations for barrier layers in metallic systems.

Outputs

Publications
R. Xie, A. Karim, J. F. Douglas, C. C. Han, and R. A. Weiss, Spinodal Dewetting of Thin Polymer Films, Physical Review Letters 81, 1251 (1998).

Y. Feng, A. Karim, R. A. Weiss, J. F. Douglas, and C. C. Han, Control of Polystyrene Film Dewetting through Sulfonation and Metal Complexation, Macromolecules 31, 484 (1998).

C. C. Han, C. Zhou, and E. K. Hobbie, Cross-Link Density and the Strength of the Binding Interaction in Hydrogen-Bonded Polymer Blends, American Chemical Society Polymeric Materials Science and Engineering Preprints 78, 141 (1998).

C. Zhou, E. K. Hobbie, B. J. Bauer, L. Sung, M. Jiang, and C. C. Han, Control of Interaction Strength in Hydrogen-Bonded Polymer Blends Via the Density of the Hydroxyl Group, Macromolecules 31, 1937 (1998).

G. Kim, C. L. Jackson, F. V. Gyldenfeldt, V. Balsamo, M. Libera, R. Stadler, and C. C. Han, Morphology Study of Polystyrene-Polybutadiene-Polycaprolactone (PS-b-PB-b-PCL) and Polybutadiene-Polycaprolactone (PB-b-PCL) and Polystyrene-Polycaprolactone (PS-b-PCL) Semicrystalline Block Copolymers, MSA Proc. 806, (1998).

C. Zhou, E. K. Hobbie, B. J. Bauer, and C. C. Han, Equilibrium Structure of Hydrogen-Bonded Polymer Blends, Journal of Polymer Science: Part B: Polymer Physics, in press.

O. Urakawa, O. Yano, Q. Tran-Cong, A. I. Nakatani, and C. C. Han, Small-Angle Neutron Scattering Studies on the Phase Behavior of Binary Polymer Blends Driven by Photoisomerization, Macromolecules, in press.

Presentations
C. C. Han, From Phase Diagram Characterization to Polymer Blends Processing: Statics, Kinetics, and Flow Field, Goodyear Tire and Rubber Co., Akron, OH, November, 1997.

C. C. Han, Small Angle Neutron Scattering Studies of Polymer Blends, National Tsing Hua University, Department of Nuclear Engineering and engineering Physics, Hsinchu, Taiwan, November, 1997.

H. Gruell, L. Sung, S. K. Satija, A. Karim, J. Douglas, H. Jinnai, T. Hashimoto, and C. C. Han, Phase Separation and Polymer Adsorption in Binary Polymer Blend Thin Films, Wetting and Self-Organization in Thin Liquid Films Conference, München, Germany, March, 1998

H. Gruell, A. Karim, L. Sung, S. K. Satija, J. Douglas, H. Jinnai, T. Hashimoto, and C. C. Han, Confinement Effects on Phase Separation in Thin Binary Polymer Blend Films, American Physical Society Meeting, Los Angeles, CA, March, 1998.

R. Xie, A. Karim, J. F. Douglas, C. C. Han, and R. A. Weiss, Spinodal Dewetting of Thin Polymer Films, American Physical Society Meeting, Los Angeles, CA, March, 1998.

C. C. Han, C. Zhou, and E. K. Hobbie, Cross-Link Density and the Strength of the Binding Interaction in Hydrogen-Bonded Polymer Blends, American Chemical Society Meeting, Dallas, TX, April, 1998.

H. Gruell, A. Karim, L. Sung, S. K. Satija, J. Douglas, H. Jinnai, T. Hashimoto, and C. C. Han, Confinement Effects on Phase Separation in Thin Binary Polymer Blend Films, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

R. Xie, A. Karim, J. F. Douglas, C. C. Han, and R. A. Weiss, Spinodal Dewetting of Thin Polymer Films, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

A. Karim, B. D. Ermi, G. Nisato, and J. F. Douglas, Computational Problems in Blend Phase Separation, NIST Workshop on Computational Problems, Gaithersburg, MD, May, 1998.

G. Kim, C. L. Jackson, F. V. Gyldenfeldt, V. Balsamo, M. Libera, R. Stadler, and C. C. Han, Morphologies of Semicrystalline Block Copolymers Based on Polycaprolactone (PCL), X-ray Microscopy Workshop, NIST, Gaithersburg, MD, May, 1998.

C. C. Han, Thermodynamics, Rheology, and Morphology of Two Phase Blends, University Bayreuth, Department of Macromolecular Chemistry, Bayreuth, Germany, June, 1998.

G. Kim, C. L. Jackson, F. V. Gyldenfeldt, V. Balsamo, M. Libera, R. Stadler, and C. C. Han, Morphology Study of Polystyrene-Polybutadiene-Polycaprolactone (PS-b-PB-b-PCL) and Polybutadiene-Polycaprolactone (PB-b-PCL) and Polystyrene-Polycaprolactone (PS-b-PCL) Semicrystalline Block Copolymers, Microscopy Society of America, Atlanta, GA, July, 1998.

C. C. Han, Thermodynamics, Rheology, and Morphology of Two Phase Blends, Hashimoto Polymer Phasing Project Symposium on Multi-component Polymers and Polyelectrolytes, Kyoto, Japan, September, 1998.

Mixing and Structure Formation Under Shear Flow

C. C. Han, F. Qiao, L. Kielhorn¹, H. S. Jeon², A. I. Nakatani, E. K. Hobbie³, K. B. Migler, and C. Huang^4
1University of Massachusetts, Amherst, Massachusetts
²Pennsylvania State University, State College, Pennsylvania
³University of Pennsylvania, Philadelphia, Pennsylvania
⁴University of Minnesota, Minneapolis, Minnesota

Objectives
The objectives are to understand the fundamental mechanisms and to explore the possible applications in the framework of mixing and morphology control of polymer blends as a function of shear rate, temperature, composition, and compatibilizer concentration. The fundamental studies are aimed at: understanding the relationship between the mean-field, the Ising, and the shear generated mean-field-like phase behavior in binary blends; explanation and possible applications for the shear induced promotion and suppression of various phase transition temperatures in blends of homopolymers and block copolymers; the effects of the shear induced distortion of fluctuation waves on phase separated morphology and the orientation of the ordered state of the block copolymers involved; the development of in-situ characterization of multiphase materials. By working in collaboration with industry, the current goal is to demonstrate the use of these characterization methods and to apply the knowledge gained from the structure-rheology relationships of multiphase systems to help determine the range of critical processing parameters for specific applications, such as molding, extruding, compounding, and dynamic phase inversion processes.

Technical Description
The success of this study could lead to a better understanding and even comprehensive prediction of morphology/property of extruded resin and molded parts. Phase inversion under shear has been studied heavily by the extrusion community from an engineering perspective. A more scientific understanding of the phenomena would be important for future polymer alloying efforts.

• The effect of shear on the phase separation temperature of binary blends, and on the order disorder transition temperature of block copolymers, will be studied as fluctuation waves are either suppressed or distorted by the shear wave.
• The shear induced morphological structure of polyisoprene with high 1,2-microstructure content and polyisoprene or polybutadiene with high 1,4-microstructure content are being studied as two-phase blends to evaluate the elastic effect in these visco-elastic fluids.
• The structure changes, especially at high shear rate will be emphasized and compared with the entangled network chain deformation and with the flow instability.
• The concept of forming string (or fibril like) morphology at lowered interfacial tension condition will be tested by the LCP/thermoplastic blends with grafting reaction on the interface to introduce block copolymers as compatibilizer.
• The use aligned rod-like LCP polymer will be explored for an elongated fibril structure to stabilize the Rayleigh instability in order to maintain a desired morphology for applications.
• Time resolved video optical microscopy will be used to study anisotropically deformed droplets under shear jump or shear quench and measure the retraction and undulation/breakup predicted by Rayleigh instability.
• Viscoelastic systems will be compared with viscous systems and also with rigid rod chain stabilized systems.
• The steady state viscosity and dynamic modulus of multiphase polymer blends will be studied to investigate the relationship between rheological properties and structure formation (domain deformation, break-up etc.).
• The phenomena of phase inversion during shear flow will be investigated. The primary focus of the work is to find a suitable polymer blend system for which these phenomena can be directly observed through microscopy and/or light scattering.
• On-line light scattering and optical microscopy techniques will be used to demonstrate the in-situ structure characterization and to locate the narrow processing window of fiber formation in a LCP/amorphous polymer blends at elevated temperature and high shear rate with a conical twin screw extruder.
• The mechanical modulus and fracture toughness are being evaluated jointly with composite group, and correlated with the morphology characterized by the on-line LS/Optical microscope apparatus for the LCP containing blends. Different LCP's will be studied with and without in-situ grafting reaction for reactive compatibilization.
• The phenomena of dynamic phase inversion under shear flow and its relationship with composition, temperature, and viscosity are being studied.

External Collaborators

A. Halasa, Y. Feng, Goodyear Tire and Rubber Company, Akron, Ohio

Don Wiff, Wright Patterson Air Force Research Lab

H. Yang, Eastman Chemical

T. P. Lodge, University of Minnesota - Collaboration and supply of block copolymers for SANS experiments on shear behavior of block copolymers in various solvents.

R. Colby, Pennsylvania State University, State College, Pennsylvania

M. D. Dadmun, University of Tennessee, Knoxville, Tennessee - Collaboration and supply of materials for shear SANS experiments on LCP materials.

F. A. Morrison, Michigan Technological University, Houghton, Michigan - Collaboration for shear SANS experiments on cylindrical diblock copolymer melts.

J. W. Mays, University of Alabama, Birmingham, Alabama - Collaboration and synthesis of material for shear SANS experiments on cylindrical diblock copolymer melts.

Accomplishments

• Work on shear behavior of blend with external added copolymer has been completed, resulting in some fundamental understanding of compatibilizer distribution under shear and phenomena of phase separation within phase separated domain/matrix morphology.
• Shear-induced behavior on solutions of block copolymers in neutral and selective solvents has been examined by SANS.
• Interface evolution in a reactively blended liquid crystal polymer/poly(ethylene terephthalate) (LCP/PET) system has been studied by FTIR, SEM and torque-time monitoring process. The effectiveness of using a multi-functional epoxy as reactive-coupler to produce compatibilizer in-situ for morphology control of this blend has been demonstrated.
• With the use of the on line LS/Optical microscope system, a narrow processing window for LCP/PET alloying has been located and optimized.
• A droplet-fiber transition has been observed in the slit channel of the extruder for the above reactively blended LCP/PET system by the in-line light scattering and optical microscopy. This is in contrast with the droplet morphology of the uncompatibilized system.
• The stability of fibrillation has been studied under different flow conditions by the LS pattern and the Optical microscopy images. The results indicate that LCP is highly oriented under proper flow conditions, and the formation of fiber microstructure is strongly dependent on the flow and interfacial conditions.
• Fracture strength has been measured by biaxial tensile testing with preliminary results showing improved mechanical properties along the machine direction.
• Phase contrast optical microscopy and light scattering experiments were performed for critical and off-critical polybutadiene/polyisoprene blends after the cessation of shear. Time evolution data of anisotropy and other quantities are being collected.
• Computer programs for time-resolved data analysis of scattering and optical microscopy results have been developed.
• Several types of relaxation behavior due to the interplay of thermodynamics and elastic behavior have been classified. A non-linear response of the system under shear has been observed; the domain structure becomes 'cleaner' with increasing shear rate and the relaxation becomes faster. This implies that mixing of polymer blends at high shear rates might actually induce more unmixing at later times if the mixed morphology is not stabilized.

Outputs

Publications
A. I. Nakatani, L. Sung, E. K. Hobbie, and C. C. Han, Shear-Induced Order in a Homopolymer Blend With Block-Copolymer Surfactant, Physical Review Letters 79, 4693 (1997).

L. Sung, A. I. Nakatani, C. C. Han, A. Karim, J. F. Douglas, and S. K. Satija, The Role of Copolymer Additives on the Phase Behavior of a Polymer Blend, Physica B 241, 1013 (1998).

M. D. Dadmun, S. Clingman, C. K. Ober, and A. I. Nakatani, The Flow Induced Structure in a Thermotropic Liquid Crystalline Polymer as Studied by SANS, Journal of Polymer Science: Polymer Physics Edition, submitted.

E. K. Hobbie, S. Kim, J. Yu, and C. C. Han, Pattern Formation and Scaling in Critical Polymer Mixtures Under Simple Shear Flow, Il Nuovo Cimento, in press.

K. B. Migler, E. K. Hobbie, and F. Qiao, In-Line Study of Droplet Deformation in Polymer Blends in Channel Flow, Journal of Polymer Science and Engineering, submitted.

Presentations
C. C. Han, Pattern Formation and Scaling in Critical Polymer Mixtures Under Simple Shear Flow, Pennsylvania State University, Dept. of Material Science and Engineering, University Park, PA, October, 1997.

H. S. Jeon, Ordering and Disordering in Multicomponent Polymer Blends, KIST, Seoul, Korea, November, 1997.

H. S. Jeon, Phase Separation and Microemulsion in Polymer Mixtures, Sogang University, Seoul, Korea, November, 1997.

C. C. Han, Morphology of Two Phase Blends Under Shear Flow, University of Akron, Department of Polymer Engineering, Akron, OH, November, 1997.

C. C. Han, E. K. Hobbie, S. Kim, and J. W. Yu, Pattern Formation and Scaling in Critical Polymer Mixtures Under Simple Shear Flow, International Micro-symposium on Polymer Physics, PP'97, Guilin, China, November, 1997.

H. S. Jeon, Morphology and Rheology in Viscoelastic Polymer Blend, KRICT, Daejon, Korea, December, 1997.

A. I. Nakatani, L. Sung, E. K. Hobbie, and C. C. Han, Shear-Induced Order in a Homopolymer Blend With Block-Copolymer Surfactant, American Physical Society Meeting, Los Angeles, CA, March, 1998.

K. A. Barnes, F. A. Morrison, A. I., Nakatani, and J. W. Mays, Shear Effects on a PS-PB Diblock Copolymer: ODT and Morphology, American Physical Society Meeting, Los Angeles, CA, March, 1998.

L. Sung, C. Huang, T. P. Lodge, A. I. Nakatani, and C. C. Han, Shear-Induced Phase Behavior of Block Copolymers in Neutral and Selective Solvents, American Physical Society Meeting, Los Angeles, CA, March, 1998.

H. S. Jeon, and C. C. Han, Relationship between Morphology and Rheology in Viscoelastic Polymer Blends, Polymers Division Poster Presentation, Gaithersburg, MD, May, 1998.

C. C. Han, H. Jeon, S. Kim, E. K. Hobbie, A. Halasa, and W. Hsu, Morphology of Two Phase Blends Under Shear Flow, ACS Rubber Division Annual Meeting, Indianapolis, IN, May, 1998.

C. C. Han, Morphology of Two Phase Blends Under Shear Flow, Princeton University, Dept. of Chemical Engineering, William W. Graessley Symposium, Princeton, NJ, May, 1998.

C. C. Han, A. I. Nakatani, S. Kim, E. K. Hobbie, and J. W. Yu, Critical Polymer Mixtures Under Shear Flow, ESRF-ILL International Workshop on Soft Matter Under Flow as Probed by Small Angle Scattering, Grenoble, France, May, 1998.

F. Qiao, K. B. Migler, E. K Hobbie, D. Liu, and C. C Han, Reactive Compatibilization and in-line Morphology Analysis of Blends of Liquid Crystal Polymer and Amorphous Polymer, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

H. S. Jeon, A. I. Nakatani, C. C. Han, W. Hsu, and A. F. Halasa, Relationship between Morphology and Rheology in Phase Separated Viscoelastic Polymer Blend under Shear Flow, Poster at Polymer Physics Gordon Research Conference, Newport, RI, August, 1998.

L. Kielhorn, H. S. Jeon, M. Muthukumar, and C. C. Han, Relaxation Behavior of Entangled Polymer Blends after the Cessation of Shear, Poster at Polymer Physics Gordon Research Conference, Newport, RI, August, 1998.

C. C. Han, A. I. Nakatani, S. Kim, E. K. Hobbie, and J. W. Yu, Co-existence Phase Composition of Polymer Blends Under Shear Flow, International Symposium on Applied Chemistry, Changchun, China, August, 1998.

C. C. Han, Morphology of Two Phase Blends Under Shear Flow, Changchun Institute of Applied Chemistry, Changchun, China, August, 1998.

Interfaces in Immiscible Multiphase Systems

A. Karim, J. F. Douglas, D. Liu, B. Bauer, and C. Han

Objectives
The objectives are to characterize interfaces in immiscible, reactive and strongly interacting homopolymer/random/ block copolymer systems for studying compatibilization effects and to test the validity of extending the binary interaction parameter theory to pseudo-ternary systems. Interface profiles will be measured in glassy polymeric systems to delineate equilibrium from non-equilibrium effects, utilizing thin film neutron and X-ray reflectometry methods.

Technical Description
Many industrially important polymer systems tend to be multiphase in nature, which are often stabilized through the addition of compatibilizing or dispersing agents. These agents are usually copolymer materials or are generated in-situ by reaction of the blend components. The thin film geometry provides ideal interfaces by which the compatibilizing effect of a copolymer can be accurately quantified. A homopolymer/random copolymer is one of the simplest representative multiphase system. Theories on interfacial characteristics exist for such systems, yet verification through controlled experimentation is lacking. A measure of the interfacial properties in such systems is important since adhesive strength and other mechanical properties of laminates hinges critically on interface width and profile shape. Knowledge of these parameters is expected to lead to improved predictive behavior for such materials. Likewise, the control and estimation of reactively generated copolymer is important to correlate structure - property relationship in reactive polymer blends.

• Measure interface profiles in deuterated poly(phenylene oxide)/styrene acrylonitrile (PPO/SAN) and poly(phenylene oxide)/styrene maleic anhydride (PPO/SMA) bilayer films as a function of AN and MA fraction and compare with predictions from binary interaction parameter theories.
• Quantify morphological characteristics of frustrated coalescence in polycarbonate/ poly(methyl methacrylate) (PC/PMMA) films using atomic force microscopy and determine reactively generated copolymer fraction using NR.
• Compare phase separation in the PC/PMMA reactive blends to PS/PB regular blends with model PS-b-PB block copolymer surfactants in the strong segregation limit.
• Characterize interfacial width in hyperbranched poly(ethylene oxazoline) (PEOX)/linear PS bilayers samples by NR to estimate entropic contribution to adhesive strength and other interfacial properties in exploratory blend materials.
• Evaluate interface profile development occurring by segmental relaxation in dPS/PS bilayers below the bulk glass transition temperature (T_g) using NR and compare with equilibrium interface widths in immiscible bilayer systems. Compare with recent theories on interfacial mobility near deformable and hard walls.

External Collaborators
G. D. Merfeld, D. R. Paul, Center for Polymer Research, University of Texas, Austin - Collaboration on NR measurements, data fitting and analysis and supply of SAN and SMA polymers.

B. Majumdar, GE Plastics, Schenectady, New York - Collaboration and supply of dPPO samples.

G. P. Felcher, R. J. Goyette, Materials Science Department, Argonne National Laboratories, Illinois - NR measurements of glassy PS interface development.

K. F. Freed, University of Chicago, Illinois - Collaboration on theoretical aspects of sub-Tg bilayer interfacial profile development.

S. K. Satija, NIST Center for Neutron Research - Collaboration utilizing NR for interface characterization of dPPO/SAN and dPPO/SMA samples.

Accomplishments

• Characterized dependence of interface profiles in dPPO/SAN and dPPO/SMA bilayer samples for full range of copolymer composition by NR. Results validate theories on applicability of binary interaction theories to these pseudo-ternary systems.
• Observed dramatic reduction of interfacial tension in thin blend films of PS/PB with less than 1% addition of PS-b-PB, leading to suppression of lateral phase separation induced surface patterns. Instead, temporal patterns corresponding to critical fluctuations are observed. These results suggest an amplification of surfactant interfacial activity in thin films due to the layered interfacial geometry.
• Characterized the interfacial width of PEOX/PS bilayers samples as a function of PEOX branching content, from linear to highly branched, using NR. Increase of branching content induced a systematic increase of the interface width. Such novel blend systems provide a means for investigating contributions to interfacial broadening arising solely from entropic variations (rather than enthalpic), a subject of significant scientific importance and controversy in recent years.
• Confirmed an inhibition of the late-stage coalescence of droplets during phase separation in PC/PMMA reactive blends as due to the presence of a surfactant layer "frustrating" phase separation. The thickness of the reactively generated copolymer layer was measured by NR. OM measurements indicate a plateau in the structure factor of the evolving droplets due to the frustration of coalescence. Factors controlling inhibited coalescence were identified and the mechanism for droplet distortions explained.

Outputs

Publications
J. F. Douglas, R. Lipman, A. Karim, and S. Granick, Models of the Influence of Excluded Volume on the Formation of Polymer Layers, American Chemical Society PMSE Proceedings 77, 644 (1997).

C. F. Majkrzak, N. F. Berk, J. Dura, S. K. Satija, A. Karim, J. Pedulla, and R. D. Deslattes, Direct Inversion of Specular Reflectivity, Physica B 248, 338 (1998).

S. K. Satija, P. D. Gallagher, A. Karim, and L. J. Fetters, Neutron Reflection of a Chemically End-Grafted Polystyrene Brush in a Binary Mixture, Physica B 248, 204 (1998).

P. D. Gallagher, S. K. Satija, A. Karim, and L. J. Fetters, Neutron Reflection from Polystyrene Brushes in a Critical Binary Mixture, Physica B, in press.

G. D. Merfeld, A. Karim, B. Majumdar, S. K. Satija, and D. R. Paul, Interfacial Thickness in Bilayers of Poly(Phenylene Oxide) and Styrenic Copolymers, Journal of Polymer Science, Part B: Polymer Physics, in press.

A. Karim, J. F. Douglas, S. K. Satija, R. J. Goyette, and C. C. Han, Phase Separation in Chemically Reactive Polymer Blend Films, Macromolecules, submitted.

Phase Behavior of Polyolefin Blends

K. B. Migler, Y. Akpalu¹, K. A. Barnes, H. S. Jeon², C. C. Han, and E. J. Amis
¹Polytechnic University, Brooklyn, New York
²Pennsylvania State University, State College, Pennsylvania

Objectives
The objectives are to maximize the benefits to suppliers and users of new metallocene catalyzed polyolefin materials for expanded commercial opportunities by providing a greater understanding of the interplay between chain architecture (branching) and ultimate morphological properties. The ultimate aim is to control crystal structure, phase morphology and surface properties based on a rational understanding of the underlying thermodynamics and kinetic processes.

Technical Description
Blends of polyolefin materials allow the supplier to customize the material for a particular end-use. The miscibility of these blends under typical processing conditions of high temperature, pressure and shear is critical to the state of the final product. The measurements of the miscibility under pressure will allow suppliers to modify their material formulation to suit a particular processing and end-use application. Final mechanical properties in polyolefin blends are strongly influenced by crystal morphology. The question of whether phase separation precedes crystallization or is caused by it remains unresolved. Control of these processes enables the intelligent choice of blend components to achieve desired final properties.

• Crystallization of a series of polyolefins via simultaneous small angle x-ray scattering and wide-angle x-ray diffraction will be studied.
• The phase separation and relative surface layering in a model compatibilized polyolefin blend will be determined via neutron and x-ray reflectivity .
• The NIST neutron scattering shear cell and the NIST pressure cell will be utilized to measure the effects of external fields on polyolefin blend interactions and miscibility.
• The origins of the composition dependence of the interaction parameter of polyolefin blends will be explored by probing the response of these systems to pressure.
• Optical and neutron scattering will be utilized to study the effects of pressure on the interaction and phase behavior of model and commercial polyolefin blends.
• Data analysis and theoretical understanding of pressure induced changes in the interaction parameter will be emphasized.
• The phase behavior between blends of polyethylene and a copolymer with side chain branching will be studied to examine the competition between crystallization and phase separation.
• Neutron scattering and small angle light scattering will be used to examine the occurrence of phase separation and the kinetics of crystallization.

External Collaborators
D. J. Lohse and M. Rabeony, Exxon Research and Engineering Company, Annandale, New Jersey - CRADA developed to measure the pressure and shear rate dependence of the phase behavior of metallocene catalyzed polyolefin blends by SANS and optical techniques.

N. Balsara, Polytechnic University, Brooklyn, New York - Special synthesis of model polyolefins and study of the effects of external fields.

Accomplishments

• Two distinct behaviors of structure growth were discovered during the early stages of crystallization using monodisperse polyethylene at low undercooling. Time resolved small and wide angle x-ray scattering (SAXS and WAXS) measurements found that in the first regime, density fluctuations increase in size and amplitude as a result of the development of local order in the sample. In the second regime, these dense regions evolve into the growing lamellar crystals. The second regime growth process is temperature dependent.
• The kinetics of crystallization in model polyolefin materials were measured as a function of short side chain branch content. Large length scale density fluctuations were found to precede the onset of crystal structure.
• In thin films (200-400 Å) of compatibilized model polyolefin blends the onset of lateral phase separation decreases with film thickness. Neutron reflectivity demonstrates that a compatibilizing agent alters the kinetics of phase separation but does not change the final shape of the density profile.

Outputs

Publications
K. B. Migler, and C. C. Han, Static and Kinetic Study of a Pressure Induced Order-Disorder Transition: Birefringence and Neutron Scattering, Macromolecules 31, 360 (1998).

M. Rabeony, D. J. Lohse, R. T. Garner, W. W. Graessley, and K. B. Migler, Effect of Pressure on Polymer Blend Miscibility: A Temperature-Pressure Superposition, Macromolecules, in press.

Presentations
Y. Akpalu, Effect of Branch Content on Spherulitic Growth in Homogeneous Ethylene-1-Octene Copolymer Blends: Time Resolved Synchrotron X-ray and Small Angle Light Scattering, American Physical Society Meeting, Los Angeles, CA, March, 1998.

In-Line Optical Characterization of Polymer Extrusion and Blend Morphology

K. B. Migler, E. K. Hobbie¹, F. Qiao, C. C. Han, and E. J. Amis
¹University of Pennsylvania, Philadelphia, Pennsylvania

Objectives

The objectives are to develop a flexible set of optical based tools for measurement of critical processing parameters and demonstrate their value to industry. Utilization of optical tools will deepen the understanding of processing phenomena which occur under high shear conditions, such as morphology development, fiber formation, and slippage.

Technical Description
Ultimate blend properties depend critically on the structural morphology. Manufacturers have little understanding of how to generate desired morphologies. This work will generate characterization of the powerful effects of normal forces on the morphology. While polymer melt processing is carried out under conditions of extreme shear stresses and normal forces, laboratory measurements of droplet morphology have been confined to the low shear regime. We have evidence of profound changes in droplet morphology as shear rates enter the processing regime.

• An extrusion slit die with optical access for in-situ microscopy and light scattering enables measurement of polymer blend morphology and polymer flow profiles.
• Microscopy permits measurements of structures in the 2 - 200 micron range while light scattering can measure structures at length scales down to 0.1 micron.
• The morphology of polymeric droplets are measured as a function of depth and shear stress in the flow channel.
• The effect on viscosity ratio on polymer deformation and breakup are measured.
• Key processing variables in the control of material structure are identified.
• The influence of processing on the development of morphology for representative classes of polymer blends are examined.
• Measurements in both the twin screw extruder and the optical cone and plate device will be continued.
• Complimentary rheological measurements in the pure homopolymers will be conducted and used to identify the relevant rheological conditions that create these unusual shapes.
• Theoretical models of the morphology utilizing normal force concepts will be developed.

External Collaborators
3M Corporation, St. Paul, Minnesota - Velocity profile measurements/Polymer processing additives.

Exxon Research and Engineering Company, Annandale, New Jersey - Measurements of polyolefin blends structure during extrusion.

Accomplishments

• Discovery of a blend system, which exhibits highly anisotropic structures in the vorticity direction, was made as part of a systematic investigation of the vorticity alignment in sheared polymeric blends. A theoretical model based on normal stress differences was developed that predicts that the onset of this novel phenomenon when the droplet first normal stress difference exceeds that of the matrix. Rheological measurements carried out on the same materials demonstrate qualitative agreement between the experiment and theory.
• A comprehensive study of morphology as a function of viscosity ratio, screw rotation rate and channel depth was completed. A dramatic effect of viscosity ratio on the creation of strings was observed. Depth resolved optical microscopy revealed that morphology of droplets is a strong function of position. In the low shear limit, local stress is the controlling parameter, whereas at high shear stress, a transition to pure droplets occurs. Discovery that the surface can act as a compatibilizing agent to create strings in the presence of shear flow.
• The first direct measurements of slippage at the melt-wall interface upon introduction of a polymer processing additive was conducted. The efficiency and performance of wall-slip additives with regards to processing optimization were investigated.
• Measurements were performed that further our fundamental understanding of the role of compatibilizers in polymer processing, particularly with regard to shear-induced structures in polymer blends and thermoplastic/polymer - liquid crystal blends.

Outputs

Publications
S. Li, K. B. Migler, E. K. Hobbie, H. Kramer, C. C. Han, and E. J. Amis, Light Scattering Photometer with Optical Microscope for the In-Line Study of Polymer Extrusion, Journal of Polymer Science: Polymer Physics Edition 35, 2935 (1997).

E. K. Hobbie, and K. B. Migler, Droplet Morphologies During Polymer Blends Extrusion, ANTEC '98, Society of Plastics Engineers, Technical Papers XLIIII, 711 (1998).

E. K. Hobbie, K. B. Migler, C. C. Han, and E. J. Amis, Light Scattering and Optical Microscopy As In-Line Probes of Polymer Blend Extrusion, Advances in Polymer Technology 17, 307 (1998).

K. B. Migler, E. K. Hobbie, and F. Qiao, In-Line Study of Droplet Deformation in Polymer Blends in Channel Flow, Journal of Polymer Science and Engineering, submitted.

E. K. Hobbie, and K. B. Migler, Negative Deformation Number in Sheared Polymeric Emulsions, Physical Review Letters, submitted.

Presentations
K. B. Migler, In-Line Optical Measurements for Polymer Processing, 3M Corporation, St. Paul, MN, 1997.

K. B. Migler, Novel Droplet Morphologies in Polymer Blends Extrusion, American Physical Society Meeting, Los Angeles, CA, March, 1998.

E. K. Hobbie, and K. B. Migler, In-Situ Visualization of Novel Polymer Droplet Morphologies During Extrusion, ANTEC '98, Atlanta, GA, April, 1998.

E. J. Amis, A. J. Bur, K. B. Migler, and E. K. Hobbie, On-line Measurements by Scattering, Microscopy, and Fluorescence, Society of Plastics Engineers ANTEC '98, New Technology Forum, Atlanta, GA, April, 1998.

E. K. Hobbie, Negative Deformation Number in Sheared Polymeric Emulsions, National Institute of Standards and Technology, Gaithersburg, MD, July, 1998.

E. K. Hobbie, Light Scattering and Optical Microscopy: Shining Light on Soft Materials, Department of Physics, Western Washington University, Bellingham, WA, 1998.

Fluorescence, Dielectrics and Ultrasonics Monitoring for Polymer Processing

A. J. Bur, K. B. Migler, S. C. Roth

Objectives
The objectives are to develop experimental methodology using fluorescence spectroscopy, ultrasonics, and dielectrics for monitoring temperature profiles, shear heating, pressure effects, molecular orientation, strain rate, and blend and filler composition as a function of processing conditions.

Technical Description

• A strain rate measurement sensor will be developed using the method of fluorescence recovery after photobleaching. We will employ the confocal optics hardware in order to obtain spatially resolved strain-rates and to focus photobleaching energy. The strain rate measurement will yield information about the viscoelastic character of a resin during flow.
• The confocal optics probe will be used to measure temperature profiles during extrusion and injection molding for various processing conditions.
• Residence times and residence time profiles will be measured as a function of position along an extruder and as a function of the depth in the flow stream. Direct industry participation is planned for this task. The experiments will be carried out in collaboration with a guest scientist from 3M Co. The confocal optics sensor will be used for the depth profiling measurements.
• A film processing machine will be instrumented with optical equipment to measure temperature and to measure the molecular orientation via fluorescence anisotropy and birefringence during the stretching phase of the process.
• The temperature and pressure behavior of fluorescence band broadening dyes will be examined by statistical, experimental, and model concepts.
• An in-line dielectric sensor will be placed on the NIST twin extruder and used to study the dielectric properties of polymer blends and filled polymers.
• Shear and longitudinal ultrasonic transducers will be developed for high temperature environments of polymer processing. Measurements of ultrasonics velocity and attenuation will be combined with models to use ultrasonics for monitoring temperature and orientation.

External Collaborators
M. McBrearty, Chemical Electrophysics Corporation, Hockessin, Delaware - Chemical ElectroPhysics will contribute dielectric spectrometer equipment and conduct experiments to measure dielectric properties of filled polymers.

M. Amon, Mobil Chemical Company, Rochester, New York - Mobil Chemical will contribute optical equipment and access to a pilot plant process line for the measurement of fluorescence anisotropy of stretched films during processing.

C. L. Thomas, Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah - The University of Utah will provide a polymer injection molding machine that will be instrumented with optical sensors for the purpose of studying physical properties of resins during molding.

Accomplishments:

• In collaboration with Chemical Electrophysics Corp., dielectric measurements of filled polymers during twin screw extrusion were performed using a new in-line dielectric sensor. The measurements yielded information about mixing ratios, residence time and sensor performance. The dielectric data are being used by Electro ChemicalPhysics Corp. to improve their dielectric sensor and to develop models for sensor behavior. The in-line application of this sensor yields real-time information about dielectric constant and dielectric loss and the composition of mixtures.
• In collaboration with Mobil Chemical, a new optical sensor was designed for real time measurements of fluorescence anisotropy during the biaxial stretching of polypropylene films that have been doped with a fluorescent dye. The sensor contains polarizing elements, focusing optics, and fiber optics for monitoring the polarization content of fluorescence radiation and for monitoring temperature using the spectral characteristics of the dye. The NIST anisotropy sensor, which is the subject of a patent application, is being used by Mobil Chemical Co. because the sensor can be deployed at high temperatures in the production oven during biaxial stretching of polypropylene film. The real-time information about molecular orientation will be used to determine final properties of the film.
• The temperature and pressure dependence of spectra from fluorescence band broadening dyes were evaluated by acquiring arrays of temperature/pressure data for four fluorescent dyes, bis di-tert-butylphenyl perylenedicarboximide (BTBP), perylene, and diphenyl octatriene (DPO) doped into PDMS and benzoxazolyl stilbene (BOS) doped into polystyrene. Statistical analysis of the data by the method of principal components is being carried out in order to separate pressure and temperature effects.
• A model for an optical interferometer sensor that was developed and employed to measure resin shrinkage during injection molding. The optical sensor that has been used to monitor injection molding has yielded multi-parameter information about resin properties including crystallization and shrinkage. Asymmetric shrinkage patterns can be used to predict warpage in the final product.

Outputs:

Publications
A. J. Bur, K. B. Migler, M. G. Vangel, and D. S. Johnsonbaugh, Real-Time Resin Temperature Measurements for Polymer Processing Using Fluorescence Spectroscopy, ASME International Eng. Cong., Dallas, 1997, Maryland-Vol. 79, p 199.

A. J. Bur, and S. C. Roth, An Optical Sensor for Measuring Fluorescence Anisotropy of Oriented Polymers, Society of Plastics Engineers ANTEC '98 Proceedings, in press. (Patent submitted to PTO for this technology).

C. L. Thomas, and A. J. Bur, Ultrasonic Melt Temperature Measurements During Extrusion, Society of Plastics Engineers ANTEC '98 Proceedings, in press.

A. J. Bur, and C. L. Thomas, In-Situ Monitoring of Product Shrinkage During Injection Molding Using an Optical Sensor, Polymer Engineering and Science, submitted.

A. J. Bur, C. L. Thomas, Optical Monitoring of Polypropylene Injection Molding, Polymer Engineering and Science, submitted.

Presentations
A. J. Bur, Real-Time Temperature Measurements for Polymer Processing Using Fluorescence Spectroscopy, American Society of Mechanical Engineering Meeting, Dallas, TX, November, 1997.

A. J. Bur, An Optical Sensor for Measuring Fluorescence Anisotropy of Oriented Polymers, Society of Plastics Engineers ANTEC '98, Atlanta, GA, April, 1998.

E. J. Amis, A. J. Bur, K. B. Migler, and E. K. Hobbie, On-line Measurements by Scattering, Microscopy, and Fluorescence, Society of Plastics Engineers ANTEC '98, New Technology Forum, Atlanta, GA, April, 1998.

Theory for Phase Separation and Transport in Polymer Liquids

J. F. Douglas, B. P. Lee, and S. C. Glotzer

Objectives
The objectives are to develop theoretical models of blend phase separation subject to perturbing influences (finite size, filler particles, shear flow) and of the transport properties of polymeric liquids with and without filler particles; to investigate and model properties of glass-forming liquids; and to provide guidance for ongoing experimental studies by the Polymer Blends and Processing Group.

Technical Description

• A general model of the viscosity of complex-shaped particle dispersions is developed based on a mathematical analogy between the hydrodynamics of concentrated particle dispersions and the problem of calculating the conductivity of a suspension of insulating particles in a conductive matrix. The use of percolation theory concepts leads to a description of the viscosity of dispersions as a function of a reduced concentration dependent on particle shape, interparticle interaction and shear rate.
• The influence of shape and surface interactions on blend phase separation is investigated numerically within a Cahn-Hilliard theory framework.
• The influence of interacting boundaries on the phase stability of compressible blends is examined by Monte Carlo simulation and analytic (mean-field) modeling of the blend phase diagram.
• Lattice Boltzmann numerical computations are utilized to evaluate the appropriateness of this technique for modeling blend phase separation. Phase separation under steady shear flow is also investigated by this method in order to compare with ongoing measurements in the Polymers Division.
• Simulations are performed to test a proposed model of the heterogeneity occurring in supercooled liquids. Analytic modeling of diffusion in supercooled liquids was performed based on effective medium theory and a model of the structural heterogeneity in supercooled liquids based on simulation observations.
• Theories of film breakup by capillary wave instability are applied to spinodal dewetting measurements. Theoretical ramifications for polymer liquids were briefly investigated to guide future measurements.

External Collaborators
J. Bicerano, Dow Chemical Company, Midland Michigan - Collaborator on modeling the transport properties of filled polymers.

N. Martys, E. Garboczi, NIST, Building and Fire Research Laboratory - Collaborator in modeling fluid phase separation by lattice Boltzmann methods.

S. Kumar, Pennsylvania State University, State College, Pennsylvania. Collaborator in modeling finite-size effects on phase separation and the glass transition.

K. Freed, University of Chicago, Chicago, Illinois - Collaborator in modeling the effect of molecular structure on polymer mixture miscibility and molecular structure effects on the glass transition.

D. Leporini, University of Pisa, Italy - Collaborator in modeling the effect fluid heterogeneity on diffusion in supercooled liquids.

Accomplishments

• The simulation of phase separation on patterned substrates indicated that surface-directed waves should form transverse to the solid substrate and that modulation of the composition should also occur in the plane of the substrate, resulting in a checkerboard composition pattern. These predictions indicated that initial polymer blend separation studies should be restricted to "ultrathin" films where the surface-directed composition waves are suppressed. The verification of the checkerboard composition pattern remains a challenge for future measurements.
• Phase separation simulations with filler particle inclusions showed the development of spherical and cylindrical composition waves developing from the inclusion boundaries. Since many commercially encountered blends have filler additives and are thermodynamically unstable these novel predicted phase separation structures likely have an important influence on the properties of these materials. These simulations provided guidance in designing experiments that confirmed simulation predictions, and are a first step in understanding how blend microstructure is affected by the presence of fillers.
• The predicted form of the viscosity of particle dispersions based on percolation concepts was validated for data involving a wide range of particle shapes. A very good approximation was found between the percolation threshold of overlapping particles and the leading concentration virial coefficient for the suspension viscosity, the intrinsic viscosity. The hydrodynamic-electrostatic analogy further indicated that the percolation threshold for rigidity, where the suspension viscosity diverges, is inversely proportional to the intrinsic viscosity. These connections provide a basis for modeling aggregating suspensions and other complex rheological problems arising in processing filled polymers. The analytic dispersion viscosity model of filled polymers is currently being utilized by industry for process design of mica platelet filled polymers. The modeling can be extended to many other properties of commercial interest (electrical and thermal conductivity, dielectric constant, and gas permeability).
• The modeling of surface confinement on a polymer blend indicated that the phase boundary can be shifted either up or down in compressible blends, depending on the strength of the polymer-surface interaction. This finding seems in accord with existing measurements, but further experiments are planned to check the theoretical predictions. The simulation and analytical modeling also predict that finite size effects on the phase boundary of polymer blends arise sooner in much thicker films than in the case of small molecule fluid mixtures. These findings indicate that finite size effects can play a significant role in the miscibility of thin polymer films increasingly utilized in applications.
• The critical properties of Lattice Boltzmann fluids (coexistence curves, surface tension, interfacial tension, correlation length, and scattering intensity) were determined and the results expressed in a form comparable to measurements on polymer blends. The critical phenomena exhibited by these computational liquids could be described by mean-field theory making the Lattice Boltzman model best suited to the description of high molecular weight blends where mean-field theory is a good approximation.
• The calculated diffusion coefficient of a particle in an inhomogeneous environment of ideally fixed obstructions was found to deviate from the Stokes-Einstein relation. This deviation arises from the different effect of the heterogeneities on the mass and momentum diffusion coefficients (viscosity). An effective medium theory indicates a fractional power relation between the viscosity and diffusion coefficient in heterogeneous fluids. Fractional Stokes-Einstein relations of this kind are commonly observed in supercooled liquids with exponents close to that predicted by the obstruction model of fluid heterogeneity. This simple model provides significant insight into the origin and nature of the anomalously large rates of diffusion observed in supercooled liquids and other heterogeneous materials.
• Theoretical models of spinodal dewetting were generalized through the introduction of a conceptual model involving three film thickness regimes defined in terms of the amplitude of equilibrium capillary waves relative to the film thickness. The formation of holes at random positions in thicker films is interpreted as a nucleation process while the random height fluctuations occurring uniformly in the thinner films reflect random phase height fluctuations similar to spinodal decomposition in polymer blends. Height fluctuations of the dewetting film correspond to composition fluctuations in the phase separating blend. This theoretical modeling has many ramifications for the problem of creating dewetted film morphologies of controlled architecture, which are important for the modification of surface properties of polymers.
• Accurate measurements of the Soret coefficient as a function of concentration were made for the first time, and universal scaling functions deduced from renormalization group theory were introduced to describe these data. Polymer solutions are particularly sensitive to temperature gradients because of the large thermophoretic forces on large macromolecules. Thermally induced concentration gradients can cause large shifts in the apparent phase boundary of polymer solutions and can give rise to complex surface pattern formation in drying polymer films. An understanding of the factors influencing the formation of defect structures in drying polymer films has many applications to polymer coatings technology.
• A new and general theory of condensed matter relaxation was introduced based on fractional calculus methods and the fluctuation theory of recurrent events. This modeling shows that classical models of exponential relaxation become generalized to a two-parameter family of functions. The two parameters of this model characterize the degree of intermittency in the relaxation process in time and the geometrical form and distribution of the material heterogeneity. This model shows promise for understanding the occurrence and form of universality in relaxation processes in condensed materials, and experiments are planned to test the proposed relaxation functions on model polymeric materials.

Outputs

Publications
J. F. Douglas, R. Lipman, A. Karim, and S. Granick, Models of the Influence of Excluded Volume on the Formation of Polymer Layers, American Chemical Society PMSE Proc. 77, 644 (1997).

B. D. Ermi, A. Karim, and J. F. Douglas, Formation and Dissolution of Phase-Separated Structures in Ultrathin Blend Films, Journal of Polymer Science, Polymer Physics Edition 36, 191 (1998).

R. Xie, A. Karim, J. F. Douglas, C. C. Han, and R. A. Weiss, Spinodal Dewetting of Thin Polymer Films, Physical Review Letters 81, 1251 (1998).

A.Karim, J.F. Douglas, B.P. Lee, S.C. Glotzer, J.A. Rogers, R.J. Jackman, E.J. Amis, and M. Whitesides, Phase Separation of Ultrathin Polymer Blend Films on Patterned Substrates, Physical Review E 57, R-6273 (1998).

B.D. Ermi, G. Nisato, J.F. Douglas, J.A. Rogers and A. Karim, Coupling Between Phase Separation and Surface Deformation Modes in Self-Organizing Polymer Blend Films, Physical Review Letters, to appear.

C. Donati, J. F. Douglas, W. Kob, S. J. Plimpton, P. H. Poole, and S. C. Glotzer, Stringlike Cooperative Motion in a Glass-forming Liquid, Physical Review Letters 80, 2338 (1998).

J. F. Douglas, and D. Leporini, Obstruction Model of the Fractional Stokes-Einstein Relation in Glass-Forming Liquids, Journal of Non-Crystalline Solids, in press.

J. F. Douglas, Polymer Science Applications of Path-Integration, Integral Equations, and Fractional Calculus, in Applications of Fractional Calculus to Physics, ed. R. Hilfer, World Scientific Press, in press.

J. F. Douglas, Coping with Complex Surfaces: An Interface Between Mathematics and Condensed Matter Physics, NRC Workshop on Exploring the Interface Between the Sciences and Mathematical Sciences, in press.

A. Karim, J. F. Douglas, S. K. Satija, R. J. Goyette, and C. C. Han, Phase Separation in Chemically Reactive Polymer Blend Films, Macromolecules, submitted.

K. J. Zhang, M. E. Briggs, J. V. Sengers, and J. F. Douglas, Thermal and Mass Diffusion in Semidilute Good Solvent Polymer Solutions, Journal of Chemical Physics, submitted.

S. Kumar, J. F. Douglas, and I. Szleifer, Critical Temperature Shifts in Thin Polymer Blend Films, Physical Review E, submitted.

G. Nisato, B. D. Ermi, J. F. Douglas, J. A. Rogers, and A. Karim, Excitation of Surface Deformation Modes in a Phase Separating Polymer Blend on a Patterned Substrate, Macromolecules, submitted.

L. Sung, A. Karim, and J. F. Douglas, Influence of Surfactant on the Structure of Phase Separated Polymer Blend Films, Macromolecules, submitted.

J. Bicerano, J.F. Douglas, and D. Brune, Model of Dispersion Rheology of Filled Polymer Liquids, Journal of Macromolecular Science: Reviews of Macromolecular Chemistry and Physics, in NIST review.

Presentations
J. F. Douglas, Effective Properties of Filled Polymer Materials, Sandia National Laboratories, Albuquerque, NM, November, 1997.

B. P. Lee, J. F. Douglas, and S. C. Glotzer, Filler-Induced Spherical Spinodal Rings in Immiscible Blends, American Physical Society Meeting, Los Angeles, CA, March, 1998.

J. F. Douglas, Coping with Complex Surfaces: An Interface Between Mathematics and Condensed Matter Physics, National Academy of Sciences Workshop, Wash. DC, March, 1998.

J. F. Douglas, Kepler's Third Law and the Swelling of Block Copolymer Layers, University of Maryland Department of Physics, College Park, MD, April, 1998.

R. Xie, A. Karim, J. F. Douglas, C. C. Han, and R. A. Weiss, Spinodal Dewetting of Thin Polymer Films, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

J. Douglas, and C. Guttman, Preliminary Results on Finite Size Effects on the Glass Transition, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

C. Donati, J. F. Douglas, W. Kob, S. J. Plimpton, P. H. Poole, and S. C. Glotzer, Observation of Polymer-like Structures in a Model Supercooled Liquid, Poster at Polymer Physics Gordon Research Conference, Newport, RI, August, 1998.

Microstructure and Dynamics of Heterogeneous Materials

S. C. Glotzer, J. F. Douglas, C. Donati, A. Al-Sunaidi¹, B. P. Lee, P. Allegrini, T. Schroeder, and S. Sastry^2
1University of Maryland, College Park
²Arizona State University

Objectives
The objectives are to demonstrate the existence of microstructural and dynamical heterogeneity in frustrated materials and phase separated blends, and to develop theoretical and computational tools to characterize heterogeneity and establish a theoretical understanding of heterogeneity.

Technical Description
The relationship between microstructure, dynamics, and properties in the broad class of "frustrated" materials is poorly understood. Demonstration of heterogeneity provides a new paradigm to describe these materials, and will allow us to develop new theories and tools that industry needs to predict material behavior. For polymer blends, these tools must account for phase separation and processing conditions, especially conditions that may be perturbative to normal phase separation.

• Computer simulations will be developed to measure and characterize heterogeneity in materials approaching a glass transition, a spinodal, or a jamming transition.
• Molecular dynamics simulations of polymer melts and other liquids will provide details inaccessible to experiments on microstructure, dynamics, and cooperative molecular motion.
• Measurements will be designed, theories tested, and realistic models of frustrated materials developed.
• Computational tools will be developed to model heterogeneous, multiphase materials under various processing conditions, with an emphasis on filled polymer blends.
• Comparisons between new Lattice Boltzmann methods and traditional Cahn-Hilliard methods for phase-separating blends will be conducted to determine the future method of choice for blend modeling.
• Simulations will be designed and performed at the Center for Theoretical and Computational Materials Science (CTCMS) in conjunction with the filled polymers project.

External Collaborators
P. H. Poole, University of Western Ontario, Department of Applied Mathematics, London, Ontario, Canada - Performed computer simulations of a glass-forming paramagnet and participated in development of measurement quantities.

S. J. Plimpton, Sandia National Laboratories, Albuquerque, New Mexico - Provided computer code for performing massively parallel computer simulations of glassforming liquids.

A. J. Liu, A. Lapena and R. Nyquist, University of California, Los Angeles, Department of Chemistry and Biochemistry, Los Angeles, California - Participated in CTCMS Heterogeneous Structures project to investigate pattern formation in polymer-dispersed liquid crystals through simulation. Contributed to theory and performed simulations and analytical calculations.

W. Kob, Johannes-Gutenberg University, Mainz, Germany - Participated in CTCMS Glasses Working group.

J. Baschnagel, Johannes-Gutenberg University, Mainz, Germany - Participated in CTCMS Glasses Working group.

C. Bennemann, Johannes-Gutenberg University, Mainz, Germany - Performed computer simulations of polymer melts.

N. Martys, NIST, Building and Fire Research Laboratory - Co-organized CTCMS workshop on Computational Methods for Modeling Multiphase Polymers.

S. A. Langer, NIST, Information Technology Laboratory - Participated in CTCMS Heterogeneous Structures project to investigate pattern formation in polymer-dispersed liquid crystals through simulation. Developed computer code and performed simulations and analytical calculations.

Accomplishments

• New theoretical and simulation ideas were developed for glassforming polymers and simple liquids that allowed the description of growing dynamical correlations for the first time. This work will lead to a fundamental understanding of slow dynamics and related phenomena in glasses and glassforming materials.
• The extent of dynamical heterogeneity in a model glassforming paramagnet was defined and calculated for the first time. Work in this program on dynamical heterogeneity in liquids and polymers is built upon the key ideas developed here.
• Dynamical heterogeneity and cooperative molecular motion in molecular dynamics simulations of glass-forming simple liquids and polymers were identified and quantified. It was shown for the first time in both systems that particle motion involves larger and larger groups of particles as temperature decreases. While this concept is at the heart of many models of glass formation, it has not been previously demonstrated. Identified the mode-coupling temperature with a percolation transition. This work will provide further insight into the physical mechanism underlying the mode coupling theory.
• A new correlation function that measures the extent to which the local molecular motion of a liquid is spatially correlated was defined. This work will provide the underpinning for a comprehensive theoretical framework to describe any system in which the local particle motions are correlated on some time scale. The work is expected to have important implications for the interpretation of data in a variety of fields, including glasses, polymeric materials, foams, polyelectrolytes, colloids, granular materials, and dense liquids.
• Simulations have shown that exploration of the potential energy landscape by a model glassforming paramagnet exhibits the same behavior as recently reported in Nature for a glassforming liquid. This result is important because it shows that the origin of slow dynamics in all frustrated systems, including polymer melts, may have a similar origin.
• Simulations have shown that the structural relaxation of a binary mixture is governed by "basin hopping" of the system on its potential energy landscape, and that basin hopping is achieved through cooperative rearrangements of groups of particles. While this idea has been discussed prominently in the literature for years, this is the first clear demonstration.
• CTCMS Multiphase Polymers working group conducted large-scale simulations to study the interference between ordering and spinodal decomposition in polymer dispersed liquid crystal (PDLC) materials, and compared resulting morphologies with those found in experiments by ALCOM and industrial researchers. Both global anisotropy and local anisotropy of PDLC domain orientation that was observed experimentally were reproduced. The results guided experimentalists in designing new "standard" experimental measurements.
• CTCMS workshop on Computational Methods for Modeling Heterogeneous Polymer Materials: A Critical Comparison, was organized and held on May 1998.

Outputs

Publications
C. Donati, J. F. Douglas, W. Kob, S. J. Plimpton, P. H. Poole, and S. C. Glotzer, Stringlike Cooperative Motion in a Glass-forming Liquid, Physical Review Letters 80, 2338 (1998).

S. C. Glotzer, A. B. MacIsaac, T. Lookman, N. Jan, and P. H. Poole, IDynamical Heterogeneity in the Ising Spin Glass, Physical Review E. 57, 7350 (1998).

S. C. Glotzer, C. Donati, and P. H. Poole, Spatially-Correlated Dynamics in Glass-forming Systems: Correlation Functions and Simulations, in "Computer Simulation Studies in Condensed Matter Physics X," ed. D. P. Landau, Springer-Verlag, 1998, in press.

P. H. Poole, C. Donati, and S. C. Glotzer, Spatial Correlations of Particle Displacements, Physica A, in press.

S. C. Glotzer, Trends in Computational Materials Science for Materials Design and Processing, National Academy of Engineering Workshop on Frontiers of Engineering, in press.

Presentations
S. C. Glotzer, Cooperative Motion and Dynamical Heterogeneity in Glassforming Materials, Workshop on Jamming in Frustrated Systems, Institute for Theoretical Physics, University of California, Santa Barbara, CA, October, 1997.

S. C. Glotzer, Dynamics of Glassforming Materials from Computer Simulation, Conference on Complex Phenomena in Physics, Barbados, West Indies, January, 1998.

S. C. Glotzer, Dynamics of Glassforming Materials from Computer Simulation, Recent Developments in Computer Simulations in Condensed Matter Physics, Athens, GA, February, 1998.

S. C. Glotzer, New Developments in Glassforming Materials, Arizona State University, Tempe, AZ, March, 1998.

S. C. Glotzer, Dynamical Heterogeneity in Glass-forming Liquids and Polymers, American Physical Society Meeting, Los Angeles, CA, March, 1998.

S. C. Glotzer, and C. Donati, Dynamical Heterogeneity in a Glassforming Polymer Melt, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

C. Donati, J. F. Douglas, W. Kob, S. J. Plimpton, P. H. Poole, and S. C. Glotzer, Stringlike Cooperative Motion in a Glass-forming Liquid, Poster at Polymer Physics Gordon Research Conference, Newport, RI, August, 1998.

S. C. Glotzer, Dynamically Heterogeneous Materials, Euro-workshop on Supercooled Liquids, Glasses and Amorphous Materials, Pisa, Italy, September, 1998.

S. C. Glotzer, Trends in Computational Materials Science for Materials Design and Processing, National Academy of Engineering Workshop on Frontiers of Engineering, Irvine, CA, September, 1998.

S. C. Glotzer, Dynamically Heterogeneous Materials, Catholic University, Johns Hopkins University, University of Maryland, University of Pennsylvania, and George Mason University.

Polymer-Filler Interactions

A. Karim, A. I. Nakatani, K. A. Barnes, E. K. Hobbie¹, R. Ivkov, D. Liu, B. J. Bauer, B. D. Ermi¹, J. F. Douglas, C. L. Jackson, and E. J. Amis
¹University of Pennsylvania, Philadelphia, Pennsylvania

Objectives
The objectives are to address critical issues hindering progress in filled polymer and nanocomposites technology by developing advanced measurement techniques suitable for quantifying filler/polymer interactions, both as to structure and dynamics, by utilizing expertise in scattering, rheology, and on-line microscopy. Concurrent modeling efforts will predict the viscosity of filled polymers as a function of filler dispersion and interactions.

Technical Description
Filled polymers and nanocomposites represent a significant share of the world plastics market. However a major limitation to further growth and development of this industry is the lack of understanding and measurements tools for interactions between the fillers and the polymer matrix. Industry is thus forced to adopt empirical approaches which usually lead to long product development cycles. Quantification of polymer-surface interactions will improve techniques for modifying polymer-surface interactions and validate models predicting material properties. Untested Monte Carlo simulations predict the radius of gyration in the presence and absence of filler particles of various sizes. Measurements of stress relaxation and local rheology of filled polymers are critical for improvements in mixing, stabilization, and performance of filled polymer materials. The most recent advance to filled polymers is the area of clay-nanocomposites where similar types of measurements are also needed for further developments in the field.

• The phase behavior of polymer blends (e.g. PS/PB) in the presence of fillers will be examined by light scattering, small angle neutron scattering (SANS), atomic force microscopy (AFM) and optical microscopy.
• SANS will be used to characterize polymer molecular dimensions, domain sizes and interaction parameters of poly(dimethyl siloxane) (PDMS) blended with treated silica fillers, and polybutadiene (PB) mixed with carbon black. Rheological tests on these systems will be used to relate scattering results and mechanical behavior.
• Model filler surfaces will be prepared on silicon wafers by depositing a carbon film, treating by plasma etching or chemical modification with coupling agents to mimic carbon black.
• Homopolymers and polymer blends will be coated on the treated surfaces and the polymer-surface interactions characterized by AFM and reflectivity. Neutron reflectivity of polymer blends with finely dispersed fillers and on model filler surfaces will be examined.
• Digital-video microscopy will be developed as a measurement technique to study kinetics, structure, collective dynamics, and viscoelastic relaxation in polymer-colloid complexes and dispersed filler particles in entangled polymers.
• The structure and dynamics (segmental and chain) of polymers such as polyethylene oxide (PEO) intercalated into clay-polymer nanocomposites will be characterized using inelastic neutron scattering techniques such as filter-analyzer spectroscopy, neutron time-of-flight and spin-echo spectroscopy.
• SANS will be utilized for investigating clay/polymer suspensions to characterize the nature of clay/polymer interactions.
• Methods will be developed to quantify and characterize the static and dynamic interactions of various polymers with the clays by x-ray and neutron reflectometry and atomic force microscopy (AFM).

External Collaborators
W. Chen, G. V. Gordon, R. G. Schmidt, Dow Corning Corporation, Midland, Michigan - Collaboration and supply of materials for experiments on chain dimensions of filled polymers and phase separation behavior of filled blends.

A. Halasa, Y. Feng, Goodyear Tire and Rubber Company, Akron, Ohio - Collaboration and supply of materials for SANS characterization of filled polymers.

B. Majumdar, GE Plastics, Schenectady, New York - Collaboration and supply of polymers for filled materials.

N. Moll, Dow Chemical Company, Midland, Michigan - Collaboration and supply of clay materials.

J. Gilman, T. Kashiwagi, NIST, Building and Fire Research Laboratory - Collaboration and supply of materials for SANS characterization of filled polypropylenes.

N. Malizsewskyi, P. Gehring, NIST Center for Neutron Research - Collaboration on inelastic neutron scattering from intercalated clays.

R. Krishnamoorti, University of Houston - Supply of clay nanocomposites for inelastic neutron scattering.

Accomplishments

• A workshop entitled "Interactions of Polymers with Fillers and Nanocomposites" was organized and held at NIST on June 18-19, 1998. Of the 75 non-NIST participants, 2/3 were industry experts in filled polymer technology. Control of molecular level interactions and measuring the dynamics of polymers at the filler interface were identified as the most critical issues in this field.
• Perturbations of polymer blend phase separation by fillers were shown to provide sensitive measures of preferential interfacial interactions. With this discovery, expertise in measurements of polymer blends can be applied to characterize polymer nanocomposites where production, as well as their high value properties, are dominated by polymer-filler interactions.
• Extensive cloudpoint measurements confirm filler induced shifts in phase boundary of polystyrene/polybutadiene (PS/PB) blends. Measurements were performed as a function of several different filler types and blend compositions. Filler types include three different fumed silicas with and without grafted polystyrene, and silica beads of 0.5 µm size, both without and with surface treatment by a silane coupling agent. Cloudpoints for the fumed silica filled sample were shifted to higher temperatures, and the extent of the shifts depended on the type of fumed silica used. The destabilization of the blend by filler is unexpected, and suggests that the interactions between the filler and PB phase are strong. These measurements demonstrate that the phase separation behavior of polymer blends is sensitive to differences in fillers undetectable by conventional means such as TEM and N2 adsorption methods currently used by industry.
• The amount of PS grafted to the fumed silica was characterized by TGA and the amount of grafted polymer was related to the cloudpoint shift in the model blend filled with fumed silica. This indicates that differences in the number of surface groups on the different fumed silicas may be responsible for the variations in the observed cloudpoint behavior.
• Characterization of the size and morphology of phase separating PS/PB and PS/PVME blends filled with fumed silica, PS latex, colloidal gold and tetrapropyl orthosilicate (TPOS) and tetraethyl orthosilicate (TEOS) based silica beads by AFM, OM, and SEM indicate different types of phase separation regimes. In the case of small particles, the blend phase separation predominates while large filler particles lead to a phase separation dominated by the wetting of these particles.
• Morphological regimes of phase separating PS/PB and PS/PVME blends were identified in thin films as a function of filler particle mobility. In order of increasing mobility, the particles included fumed silica, silica beads (commercial and synthesized), colloidal silicas, colloidal gold, and bucky balls.
• In the limit of low filler mobility, wetting of the filler by one component dominates and pins the blend morphology. At the other extreme of high filler mobility, blend phase separation dominates the process. In the cases of intermediate mobility, both interfacial segregation and temporal phase migration of filler are observed.
• A TEM staining technique was developed and it was found that the fumed silica surface is preferentially wetted by the PB phase (stained with OsO₄).
• Small angle neutron scattering measurements were performed on fumed silica filled polybutadienes with four different surface treatments at a fixed concentration of coupling agent as well as five different concentrations of the coupling agent with a fixed surface treatment. The filled samples with different coupling agent concentrations were mixed under two different mixing protocols. No differences in the scattering were observed for all conditions tested, suggesting that correlations in filled homopolymer systems are unaffected by filler surface treatment.
• Preliminary observations indicated suppression of dewetting by addition of trace amounts of bucky balls to thin PS and PB films. This phenomenon has important implications for thin film inhibiting defects in polymer coatings.
• SANS measurements were performed on three component mixtures of labeled PDMS, unlabeled PDMS, and filler. An analysis scheme was developed for extraction of the single chain structure factors of each polymer component by assuming the filler can be treated as a solvent molecule. From the analysis, the single chain dimensions of labeled and unlabeled polymers larger than the filler particle size increase at low filler concentrations (mass fractions<0.10) then decrease to values slightly larger than the unfilled dimensions at higher filler concentrations. for polymers approximately the same size as the filler particles, the chain dimensions are slightly smaller than the unfilled chain dimensions.
• Neutron measurements have shown that confinement of polymer chains to spaces (~1.4 nm) that accompany intercalation in nanocomposites significantly restricts the mobility of the chains. An increase of only 0.4 nm in the spacing can produce a noticeable change in the polymer chain mobility, so that some bulk polymer features are recovered.
• Methods were established to prepare clay (laponite)/polymer films on silicon with varied and controlled thickness and to characterize them by x-ray reflectivity and atomic force microscopy. Potential applications for creating ordered nanostructure coatings and for opportunities for investigating structure and interactions between clay and polymer under more ideal conditions are evident through these studies.
• SANS observation on PAA-clay in solutions where the long range ordering is suppressed under the influence of shear, provided important structural information on clay-polymer suspensions. This demonstrates the potential utility of SANS for measuring clay-polymer interactions.

Outputs

Publications
E. K. Hobbie, and M. J. Holter, Depletion Force Kinetics in Confined Colloidal Mixtures, Journal of Chemical Physics 108, 2618 (1998).

A. I. Nakatani, W. Chen, R. G. Schmidt, G. V. Gordon, and C. C. Han, Chain Dimensions in Polysilicate-Filled Poly(Dimethylsiloxane, American Chemical Society PMSE Division Preprints 79, 297 (1998).

E. K. Hobbie, Metastability and Depletion Driven Aggregation, Physical Review Letters, in press.

Presentations
E. K. Hobbie, K. A. Barnes, and A. I. Nakatani, Spinodal Decomposition in a Polymer Blend With Fumed Silica Inclusions, American Physical Society Meeting, Los Angeles, CA, March, 1998.

A. Karim, D. Liu, K. A. Barnes, and A. I. Nakatani, Pattern Formation in Phase Separating Polymer Blend Films with Fumed Silica Particles, American Physical Society Meeting, Los Angeles, CA, March, 1998.

E. K. Hobbie, Kinetics of Depletion Driven Aggregation in Confined Colloidal Mixtures, American Physical Society Meeting, Los Angeles, CA, March, 1998.

E. K. Hobbie, K. A. Barnes, D. Liu, A. I. Nakatani, and A. Karim, Effects of Fillers on Blend Phase Separation, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

R. Ivkov, Dynamics of Polymers in Confined Geometry: Neutron Studies of Intercalated Clay-Polymer Nanocomposites, NIST Workshop on Interactions of Polymers with Fillers and Nanocomposites, Gaithersburg, MD, June, 1998.

A. I. Nakatani, W. Chen, R. G. Schmidt, G. V. Gordon, and C. C. Han, Chain Dimensions in Polysilicate-Filled Poly(Dimethylsiloxane), American Chemical Society Meeting, Boston, MA, August, 1998.

A. Karim, E. K. Hobbie, K. A. Barnes, D. Liu, and A. I. Nakatani, Phase Separation of Polymer Blends with Fillers, American Chemical Society Meeting, Boston, MA, August, 1998.

Phase Separated Polymer Blend Coatings and Thin Films

A. Karim, B. D. Ermi¹, J. F. Douglas, D. Liu, G. Nisato¹, B. P. Lee, and S. C. Glotzer
¹University of Pennsylvania, Philadelphia, Pennsylvania

Objectives
The objectives are to develop techniques and methodologies for controlling surface adhesion and wetting in thin films by characterizing pattern formation in polymer blend films through phase separation, substrate patterning and surface reaction. Utilize surface probe microscopy (SPM) techniques such as atomic force microscopy (AFM) and near surface optical microscopy (NSOM) as measurement tools for characterization of nanoscale pattern formation.

Technical Description
A quantitative technique for measuring kinetics and morphology development through phase separation in thin polymer blend films is vital for validating any predictive model or theory on wetting and adhesion of blends on surfaces. Scanning probe microscopy (SPM) provides unique opportunities for characterizing phase separation phenomena in real space. Identifying the important controlling factors affecting localized blend phase separation in the vicinity of heterogeneous surfaces is important since most real surfaces tend to be heterogeneous.

• The kinetics and morphology of phase separation of PS/PB and PS/PVME blend films on homogeneous and patterned self-assembled monolayer (SAM) surfaces will be characterized using a combination of AFM, optical microscopy (OM), and neutron reflection (NR).
• Regimes of blend film thickness defining transitions in the nature and alignment of induced patterns through pattern-directed phase separation will be identified. The possibility of creating patterned spinodally-dewet films will be investigated.
• 2-D FFT analysis methods already developed for optical image studies will be extended to analysis of AFM topographical data from blends on patterned surfaces. The kinetics of isotropic phase separation will be discriminated from the anisotropic morphology evolution by selective averaging of the 2-D FFT data.
• Equilibrium analytical theory will be used to predict aspect ratio of steady state laterally phase-separated structures. Modified Cahn-Hilliard-Cook (CHC) based computer simulations will be used for predicting the morphology of phase separating mixture films on periodically modulated surfaces. Experimental results from model blend films of varying composition and thickness will be used to validate the analytical model and simulations of ultrathin film phase separation on patterned surfaces.
• Nucleation and growth versus spinodal decomposition regimes in blend films will be distinguished by varying blend composition and studying changes in film morphology. Two-phase to single phase temperature jump measurements will be performed to test reversibility of surface topology for the different blend compositions.
• NSOM will be used to investigate sub-surface morphology development in phase separated conducting/non-conducting (thiophene/PS) polymer blend films prepared by spin coating.

External Collaborators
G. M. Whitesides, R. J. Jackman, Department of Chemistry, Harvard University, Cambridge, Massachusetts - Supply of SAM patterned substrates.

J. A. Rogers, Lucent Technologies, Murray Hill, New Jersey - Collaboration and supply of SAM patterned substrates.

M. Walker, NIST, Surface and Microanalysis Division - Phase-mode AFM characterization of coating films.

L. Goldner, NIST, Physics Division - Near surface optical microscopy (NSOM) measurements of phase separated blend films

Accomplishments

• A coupling was discovered between phase separation and surface deformation modes of phase separating blends on chemically patterned self assembled monolayer (SAM) substrates. The surface deformation modes induced by phase separation contain excited transient harmonics, which are close to the harmonics of the SAM pattern. Recognition of the SAM pattern by the phase separating blend thus occurs at early times when the phase separation length scale is only a fraction of the SAM pattern scale (few µm).
• The perfection of steady state alignment of the morphology of a phase separated blend to an underlying SAM pattern was demonstrated as a function of decreasing film thickness. Furthermore, the reduction in film thickness below a critical value was shown to cause a break-up of the aligned strips into uniform droplets via spinodal dewetting. This phenomenon produces aligned nano-droplet arrays, a process that may be technologically significant for applications requiring control of surface wetting properties at the nanometer level.
• A theoretical perspective for coupling between phase separation and surface deformation modes in terms of theory of shallow fluid channels was developed. An analytical model for predicting steady state topography of blend films of PS/PB, PS/PVME and poly(ethylene propylene (PEP)/dPEP in terms of surface and interfacial tension ratios was verified. Computer simulations of phase separation with periodic surface modulations using modified CHC equations were used to generate novel transverse checkerboard blend composition profiles in 2-D.
• Thermodynamic reversibility of phase separated structures in thin films for all compositions was demonstrated. The kinetics of the dissolution process was different from the phase separation process for the same quench depth conditions. These measurements confirm the phase separation origin of surface modulated structures in thin blend films.
• Preliminary success was achieved in the characterization of sub-surface phase distribution of polythiophene in PS matrix (chemical sensitivity) using NSOM with sub-micron resolution. Such non-destructive determination of polymer phase distribution in thin films is not possible by conventional microscopy techniques.

Outputs

Publications
B. D. Ermi, A. Karim, J. F. Douglas, and L. Sung, Atomic Force Microscopy Investigations of Phase Separation in Ultrathin Polymer Blend Films, American Chemical Society PMSE Proceedings 77, 606 (1997).

A. Karim, T. M. Slawecki, S. K. Kumar, J. F. Douglas, S. K. Satija, C. C. Han, T. P. Russell, Y. Liu, R. Overney, J. Sokolov, and M. H. Rafailovich, Phase Separation Induced Surface Patterns in Thin Polymer Blend Films, Macromolecules 31, 857 (1998).

A. Karim, J. F. Douglas, B. P. Lee, S. C. Glotzer, J. A. Rogers, R. J. Jackman, E. J. Amis, and G. M. Whitesides, Phase Separation of Ultrathin Polymer Blend Films on Patterned Substrates, Physical Review E 57, R6273 (1998).

B. D. Ermi, A. Karim, and J. F. Douglas, Formation and Dissolution of Phase-Separated Structures in Ultrathin Blend Films, Journal of Polymer Science, Polymer Physics Edition 36, 191 (1998).

A. Karim, Ed., "Surfaces, Interfaces and Thin Films," Directions in Condensed Matter Physics Series, World Scientific Publishing Co., Inc., in press.

B. D. Ermi, G. Nisato, J. F. Douglas, J. A. Rogers, and A. Karim, Coupling Between Phase Separation and Surface Deformation Modes in Self-Organizing Polymer Blend Films, Physical Review Letters, in press.

Presentations
A. Karim, B. D. Ermi, G. Nisato, and J. F. Douglas, Formation and Dissolution of Phase Separated Structures in Polymer Blend Films, Materials Research Society Meeting, Boston, MA, December, 1997.

A. Karim, B. D. Ermi, G. Nisato, and J. F. Douglas, Coupling of Phase Separation and Surface Excitation Modes on Patterned Surfaces, American Physical Society Meeting, Los Angeles, CA, March, 1998.

A. Karim, B. D. Ermi, G. Nisato, and J. F. Douglas, Phase Separation of Polymer Blends on SAM Patterned Surfaces, 2^nd International Workshop on Wetting and Self-Organization in Thin Liquid Films, Munich, Germany, March, 1998.

A. Karim, B. D. Ermi, G. Nisato, and J. F. Douglas, Computational Problems in Blend Phase Separation, NIST Workshop on Computational Problems, Gaithersburg, MD, May, 1998.

B. Ermi, G. Nisato, J. F. Douglas, and A. Karim, Manipulation and Control of Microscopic Patterning of Polymer Films Through Guided Growth, NIST Polymers Division Poster Session, Gaithersburg, MD, May, 1998.

A. Karim, and G. P. Felcher, Neutron Reflection for Probing Interfacial Profiles, American Crystallographic Association, Crystal City, VA, July, 1998.

B. D. Ermi, Development of Measurement Tools to Characterize Polymer Films and Polyelectrolyte Solutions, Aristech Chemical Company, Pittsburgh, PA, July, 1998.

B. D. Ermi, G. Nisato, J. F. Douglas, and A. Karim, Polymer Blend Film Phase-Separation on Patterned SAM substrates, American Chemical Society, Boston, MA, August, 1998.

B. D. Ermi, Development of Measurement Tools to Characterize Polymer Films and Polyelectrolyte Solutions, General Electric, Mt. Vernon, IN, September, 1998.

Characterization of Dendrimers with Polymers, Metals, and Small Molecules

B. J. Bauer, F. Groehn¹, A. Ramzi², T. J. Prosa, D. Liu, A. Topp³, C. L. Jackson, K. A. Barnes, A. Karim, G. Nisato⁴, Y. Zhang⁵, and E. J. Amis
¹Max Planck Institute of Colloids and Interfaces, Teltow, Germany
²DSM Corporation, The Netherlands
³University of Köln, Germany
⁴University of Pennsylvania, Philadelphia, Pennsylvania
⁵Chinese University of Hong Kong

Objectives
The objectives are to characterized materials containing dendrimers with other polymers, small molecules, and metals, with regard to their assembly in bulk, in solution, and on surfaces. Dendrimer size and shape will be characterized in order to calibrate analytical methods and equipment and to explore applications of dendrimers as unique and precise macromolecules.

Technical Description
Dendrimers studied in solution have demonstrated the ability to solubilize, encapsulate, and present functional groups but little is known about immobilizing them in a polymeric matrix. Such incorporation would lead to stable nanoscopic structures. Incorporation of metals into the dendrimers would lead to materials with unique electronic and magnetic properties. Dendrimers modified with molecules such as fatty acids can emphasize their micellar character and further promote dispersion of materials. Characterization of dendrimers shows that their uniformity in size and shape makes them excellent candidates for standards in the critical 1 to 15 nm size range.

• Produce and characterize molecularly dispersed dendrimers in polymeric matrices by blending and interpenetrating polymer network (IPN) techniques.
• Characterize fatty acid modified dendrimers in bulk and in solution and in blends for both single chain structure and multi-chain morphology.
• Produce and characterize metal containing dendrimers
• Measure the dendrimers size variation in solvents of different quality and in aqueous solutions of different pH and ionic strengths.

External Collaborators
Dendritech and Michigan Molecular Institute, Midland, Michigan - CRADA developed for supply of materials, custom synthesis and joint research.

DSM - Collaboration has been established for supply of materials and a guest researcher spent 7 months at NIST on joint research.

Army Research Office - Grant (35109-CH) for work on dendrimer blends; Collaboration with Army scientists.

M. Gauthier, University of Waterloo - Collaboration has been established for supply of materials for joint research.

N. Mishenko, Catholic University of Leuven - Collaboration has been established to spend part of a year at NIST doing SANS of supplied materials.

I. Gitsov, Cornell University, Ithaca, New York - Collaboration has been established to time at NIST doing SANS of supplied materials.

M. Diallo, California Institute of Technology/Howard University - Collaboration has been established to spend part of a year at NIST doing SANS of supplied materials.

C. Gorman, North Carolina State University - Collaboration has been established for supply of materials for joint research.

H. D. Chanzy, CERMAV and CNRS, Grenoble, France - TEM of dendrimers

F. P. Booy, Laboratory of Structural Biology, NIAMS, NIH, Bethesda, Maryland - Cryo-TEM of dendrimers

Accomplishments

• A workshop was organized and held on July 9-10 on the properties and applications of dendritic polymers. All of the dendrimer producers and many of the dendrimer users and resellers were represented. Lack of knowledge about the properties of dendritic polymers at interfaces was identified as a critical barrier to full exploitation of these unique polymers. Other needs identified by the attendees included direct comparisons of structures of dendritic polymers and characterization of interactions with other polymers.
• PAMAM dendrimers were uniformly dispersed in IPN's of hydroxyethylmethacrylate up to 25% by mass. TEM of thin sections show the dendrimers were well dispersed and visible as individual molecules, in good agreement with SAXS results. This is the first confirmation of large PAMAM dendrimers molecularly dispersed in a polymeric matrix.
• The characterization of PAMAM dendrimer molecules was achieved for generation ten (G10) to generation five (G5), ranging in size from 14.7 nm to 4.5 nm, respectively. SANS, SAX and TEM characterizations were combined for complete analysis of size, shape, and molecular conformation. These measurements establish PAMAM dendrimers as the most thoroughly characterized dendritic molecules to date.
• Methods have been developed to characterize the nanoscale phase structure of fatty acid modified dendrimers. Contrast matching methods with SANS were successful in measuring the size of different parts of these dendrimers in solution and bulk.
• Fatty acid modified dendrimers have been shown by SANS to be immiscible with polyolefins on a molecular scale, even though they can disperse pigments on a much larger size scale. This proves that miscibility is not the primary criterion in dispersion techniques.
• The structure of dendrimers with Fe covalently bound to the core was determined by SAXS. Dendrimers with attached Au were prepared and characterization of bulk and surface structures has begun.
• The size of dendrimers of a variety of generations has been measured in a complete range of solvents and varies by 10% or less over the whole series. Dendrimer size response to variations of ionic strength, pH, and presence of polymer was measured using SANS. The radius of gyration of G8 PAMAM dendrimers is rather insensitive to the solution environment, making them suitable for characterization and use as size standards.
• Small quantities of dendritic materials have a large impact on the rheological properties of PS/PVME blends. Continuing work is aimed at showing that the rheological changes are beyond the demonstrated enhancement shown with industrial fillers in blends and that these additions effect the morphology of phase separation in the blend.
• SANS on branched PS was used to determine effect of branching on miscibility with linear polymers and on size in blends and different in solvents. The fact that the highly branched PS has a smaller size in blends than it does in solution suggests that small molecules penetrate dendrimers more easily than linear polymers.
• Polyelectrolyte behavior of charged PAMAM (G5) dendrimer solutions was investigated using SANS. Repulsive interactions between dendrimers were always present even at very high (monovalent) salt concentration, in contrast to latex particles and surfactant micelles.

Outputs

Publications
T. J. Prosa, B. J. Bauer, E. J. Amis, D. A. Tomalia, and R. Scherrenberg, A SAXS Study of the Internal Structure of Dendritic Polymer Systems, Journal of Polymer Science, Polymer Physics 35, 2913 (1997).

A. Topp, B. J. Bauer, and E. J. Amis, Small Angle Neutron Scattering from Dilute and Concentrated DAB(PA)_x Dendrimer Solutions, American Chemical Society PMSE Proceedings 77, 82 (1997).

B. J. Bauer, A. Topp, T. J. Prosa, E. J. Amis, R. Yin, Q. Qin, and D. A. Tomalia, SANS and SAXS Investigations of the Internal Structure of Dendritic Molecules, American Chemical Society PMSE Proceedings 77, 87 (1997).

A. Karim, D. W. Liu, B. J. Bauer, J. F. Douglas, E. J. Amis, and D. A. Tomalia, Influence of Generation Number on the Formation of Dendrimer Monolayer, American Chemical Society PMSE Proceedings 77, 181 (1997).

E. J. Amis, A. Topp, B. J. Bauer, and D. A. Tomalia, SANS Study of Labeled PAMAM Dendrimer, American Chemical Society PMSE Proceedings 77, 183 (1997).

C. L. Jackson, H. D. Chanzy, F. P. Booy, D. A. Tomalia, and E. J. Amis, Characterization of Dendrimer Molecules by Staining and Cryoelectron Microscopy Techniques, American Chemical Society PMSE Proceedings 77, 222 (1997).

D. E. Valachovic, B. J. Bauer, E. J. Amis, and D. A. Tomalia, Dendrimer End Group Localization Determined by Counterion Mirroring, American Chemical Society PMSE Proceedings 77, 230 (1997).

J. F. Douglas, R. Lipman, A. Karim, and S. Granick, Models of the Influence of Excluded Volume on the Formation of Polymer Layers, American Chemical Society PMSE Proceedings 77, 644 (1997).

B. J. Bauer, A. Topp, T. J. Prosa, D. Liu, C. L. Jackson, and E. J. Amis, Small Angle Scattering Studies of Dendrimer Blends and Interpenetrating Polymer Networks, Society of Plastics Engineers ANTEC 98, 2065 (1998).

E. J. Amis, B. J. Bauer, et al., Preparation and Characterization of Polymer/Dendrimer Blends, Progress Report, 3/31/98, NISTIR 6151 (1998). E. J. Amis, B. J. Bauer, et al., Preparation and Characterization of Polymer/Dendrimer Blends, Progress Report, 2/24/97, NISTIR 6183 (1998).

B. J. Bauer, A. Topp, D. A. Tomalia, and E. J. Amis, Effect of Solvent Quality on the Molecular Dimensions of PAMAM Dendrimers, American Chemical Society PMSE Proceedings 79, 312 (1998).

T. J. Prosa, B. J. Bauer, A. Topp, E. J. Amis, and R. Scherrenberg, Size Changes and Interpenetration within Concentrated Dendrimer Solutions, American Chemical Society PMSE Proceedings 79, 307 (1998).

A. Ramzi, B. J. Bauer, R. Scherrenberg, J. Joosten, and E. J. Amis, SANS Study of Fatty Acid Modified Dendrimers, American Chemical Society PMSE Proceedings 79, 382 (1998).

G. Nisato, R. Ivkov, B. J. Bauer, and E. J. Amis, Characterization of Charged PAMAM Dendrimer Interactions in Solution by Small Angle Neutron Scattering, American Chemical Society PMSE Proceedings 79, 338 (1998).

C. L. Jackson, H. D. Chanzy, F. P. Booy, B. J. Drake, D. A. Tomalia, B. J. Bauer, and E. J. Amis, Visualization of Dendrimer Molecules by Transmission Electron Microscopy (TEM): Staining Methods and Cryo-TEM of Vitrified Solutions, Macromolecules 31, 6259 (1998).

Presentations
C. L. Jackson, Characterization of the Structure of Dendrimer Molecules by Transmission Electron Microscopy and Scattering Techniques, North Carolina State University, Materials Science and Engineering Department, Raleigh, NC, October, 1997.

E. J. Amis, Probing Dendrimers by Light, Neutron, and X-Ray Scattering, State University of New York at Stony Brook, Department of Chemistry, Stony Brook, NY, October, 1997.

E. J. Amis, Polymers of Unique Proportion: Characterizing Dendrimers with Neutrons, X-Rays, and Light, Materials Research Society, North Carolina Section, Research Triangle Park, NC, November, 1997.

E. J. Amis, Polymers of Unique Proportion: Characterizing Dendrimers with Neutrons, X-Rays, and Light, 3M Corporation, St. Paul, MN, January, 1998.

G. Nisato, Structure of Charged Dendrimer Solutions as Studied by SANS, Poster at Gordon Research Conference, Colloidal, Macromolecular and Polyelectrolyte Solutions, Ventura, CA, February, 1998.

T. J. Prosa, B. J. Bauer, and E. J. Amis, SAXS Analysis of Dilute Dendrimer Solutions: From Stars to Spheres, American Physical Society National Meeting, Los Angeles, CA, March, 1998.

B. J. Bauer, A. Topp, T. J. Prosa, D. Liu, C. L. Jackson, and E. J. Amis, Small Angle Scattering Studies of Dendrimer Blends and Interpenetrating Polymer Networks, Society of Plastics Engineers, ANTEC '98, Atlanta, GA, April, 1998.

B. J. Bauer, Small Angle Scattering Studies of Dendrimer Blends and Interpenetrating Polymer Networks, ANTEC '98, Atlanta, GA, April, 1998.

B. J. Bauer, Dendritically Branched Polymer Solutions and Blends, Army Research Laboratories, Aberdeen, MD, April, 1998.

E. J. Amis, Dendrimers: Polymers of Unique Dimension, Taniguchi Conference on Polymer Science Toward the 21st Century, Kyoto, Japan, May, 1998.

E. J. Amis, Dendrimers: Polymers of Unique Dimension - Characterization by Light, X-Ray, and Neutron Scattering, Stanford University, Department of Chemical Engineering, Palo Alto, CA, June, 1998.

E. J. Amis, B. J. Bauer, A. Topp, and T. Prosa, Dendrimers as Microgels and Segments of Macrogels, International Polymer Networks 98, Trondheim, Norway, June, 1998.

B. J. Bauer, Dendrimer Characterization, Unique Properties: Characterization by SAXS, SANS and TEM, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

G. Nisato, Polyelectrolyte Dendrimers as Model Spherical Colloids, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

A. Topp, B. J. Bauer, and E. J. Amis, Small Angle Neutron Scattering from Dilute and Concentrated DAB(PA)_x Dendrimer Solutions, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

C. L. Jackson, H. D. Chanzy, and F. P. Booy, Characterization of Polymer Micellar Suspensions and Dendrimer Solutions by Cryo-electron Microscopy, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

B. J. Bauer, A. Topp, D. Valachovic, D. Liu, and E. J. Amis, SANS of Labeled Dendrimer Solutions, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

B. J. Bauer, A. Topp, T. J. Prosa, D. Liu, C. L. Jackson, and E. J. Amis, Small Angle Scattering Studies of Dendrimer Blends and Interpenetrating Polymer Networks, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

A. Karim, D. W. Liu, B. J. Bauer, J. F. Douglas, and E. J. Amis, Influence of Generation Number on the Formation of Dendrimer Monolayers, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

S. Choi, R. M. Briber, B. J. Bauer, A, Topp, and M. Gauthier, Arborescent Graft Polymers, Workshop on Properties and Applications of Dendritic Polymers, Gaithersburg, MD, July, 1998.

E. J. Amis, B. J. Bauer, A. Topp, and T. J. Prosa, Dendrimers: Polymers of Unique Dimension, Poster at Polymer Physics Gordon Research Conference, Newport, RI, August, 1998.

B. J. Bauer, Effect of Solvent Quality on the Molecular Dimensions of PAMAM Dendrimers, American Chemical Society Meeting, Boston, MA, August, 1998.

R. Ivkov, Characterization of Charged PAMAM Dendrimer Interactions in Solution by Small Angle Neutron Scattering, American Chemical Society Meeting, Boston, MA, August, 1998.

A. Ramzi, SANS Study of Fatty Acid Modified Dendrimers, American Chemical Society Meeting, Boston, MA, August, 1998.

B. J. Bauer, Size Changes and Interpenetration within Concentrated Dendrimer Solutions, American Chemical Society Meeting, Boston, MA, August, 1998.

E. J. Amis, Dendrimers: Polymers of Unique Dimension, Kyushu University, Department of Polymer Science, Fukuoka, Japan, August, 1998.

E. J. Amis, Dendrimers: Polymers of Unique Dimension, Osaka University, Department of Macromolecular Science, Osaka, Japan, September, 1998.

Polymer Solutions

E. J. Amis, G. Nisato¹, Y. Zhang², R. Ivkov, B. J. Bauer, D. Liu, and B. D. Ermi^1
1University of Pennsylvania, Philadelphia, Pennsylvania
²Chinese University of Hong Kong

Objectives
The objectives are to develop measurement methods to characterize the interactions of polymers in solution and their properties as stabilizers, flocculants, rheology modifiers, and gels. New experimental methodology recently developed at NIST will be applied to characterize the mechanisms of polyelectrolyte interactions with simple ions, macroions, neutrals, and surfaces.

Technical Description
Aqueous solutions and gels represent a growing polymer market and polyelectrolytes comprise the major class of water compatible polymers. Although polyelectrolytes are notoriously difficult to characterize, their most dramatic properties are nearly universal and therefore new measurement methods and descriptions of properties will have a broad impact. Recent experimental and theoretical advances offer this promise. Associative polymers are widely used by industry as viscosity modifiers in food, consumer products, and industrial fluids. Improved characterization and methods of characterization will enhance both quality control and ability to predict behavior of new formulations.

• The critical issue of competitive long and short range interactions in polyelectrolyte solutions will be characterized by SANS, SAXS, and LS.
• Contrast labeling methods will be developed to measure systems that model classes of behavior representative of commercially important polyelectrolyte solutions.
• The effects of counterion charge, polyion molar mass, and variations with charge density will be characterized.
• Associative polymers and their transient gels will be measured by the combination of scattering and rheology to characterize mechanisms of shear thickening, thinning, and gelation.
• Thermoreversible polyolefin physical gels of ethylene/propylene copolymers will be characterized in organic solvents and in simulated motor oil.

External Collaborators
A. Gast, J. Hur, J. Pople, R. Waymouth, Department of Chemical Engineering, Stanford University, Center for Polymer Interfaces and Macromolecular Assemblies, Stanford, California - Collaboration on structure, rheology and mixing in polymer/colloid suspensions; Collaboration on network structure in metallocene polymerized thermoplastic polyolefins.

T. Jao, C. Daniel, Ethyl Corporation, Richmond, Virginia - Collaboration on mechanism of oil additive gelation; Synthesis of deuterated copolymers; Joint measurements at NIST

Accomplishments

• Large differences were shown for the types of gels formed from ethylene/propylene copolymers with small variations of ethylene content in toluene and methyl cyclohexane. Such differences are reflected in significant rheological changes which are important for applications as motor oil additives. The understanding gained from these studies is being used by industry to develop new products that prevent low temperature oil gelation.
• Single chain dimensions of polyelectrolytes without added salt were measured as a function of concentration, polymer molar mass, and valency of the counterion in dilute, semidilute and concentrated solutions by the neutron zero-average-contrast method. The chain dimensions and scaling with molar mass show features of semiflexible rods in the presence of monovalent counterions and random coils in the presence of divalent counterions. Neither extreme of rod-like expansion or coil collapse is observed at finite concentration.
• The microstructure of salt free polyelectrolyte solutions throughout the semidilute regime was shown to be determined by the valency, rather than the size or the chemical identity of the counterions. This observation is linked directly to previous work at NIST showing that long range and short range electrostatic interactions, as opposed to hydrophobic interactions, dominate the structure and dynamics of these solutions.
• The polyelectrolyte behavior characterized by the correlation peak in the SANS profile, was found to show a continuous growth and transition with increasing charge density from neutral poly(2-vinylpyridine) to charged poly(N-methyl-2-vinylpyridinium chloride). The peak position was found to vary as Cp^alpha with alpha increasing with the charge density.

Outputs

Publications
B. D. Ermi and E. J. Amis, Influence of Backbone Solvation on Small Angle Neutron Scattering from Polyelectrolyte Solutions, Macromolecules 30, 6937 (1997).

B. D. Ermi, Y. Zhang, and E. J. Amis, Counterion Valence Effects on Inter- and Intramolecular Interactions in Polyelectrolyte Solutions, American Chemical Society PMSE Proceedings 77, 304 (1998).

B. D. Ermi and E. J. Amis, Domain Structures in Low Ionic Strength Polyelectrolyte Solutions, Macromolecules, 31, 7378 (1998).

Presentations
E. J. Amis, Structure and Dynamics in Polyelectrolyte Solutions, University of Maine, Department of Chemical Engineering, Orono, ME, November, 1997.

E. J. Amis, Shining New Light (and Neutrons) on the Puzzles of Polyelectrolytes, North Carolina State University, Materials Science and Engineering, Raleigh, NC, November, 1997

E. J. Amis, Shining Light (Neutrons and X-Rays) on the Puzzles of Polyelectrolytes, Gordon Research Conference, Colloidal, Macromolecular and Polyelectrolyte Solutions, Ventura, CA, February, 1998.

Y. Zhang, Small Angle Neutron Scattering Studies of Polystyrene Sulfonate Solutions with Mono- and Divalent Counterions, Poster at Gordon Research Conference, Colloidal, Macromolecular and Polyelectrolyte Solutions, Ventura, CA, February, 1998.

R. Ivkov, SANS Investigation of the Structure and Equilibrium Polymerization of Muscle Actin, Poster at Gordon Research Conference, Colloidal, Macromolecular and Polyelectrolyte Solutions, Ventura, CA, February, 1998.

G. Nisato, Structure of Charged Dendrimer Solutions as Studied by SANS, Poster at Gordon Research Conference, Colloidal, Macromolecular and Polyelectrolyte Solutions, Ventura, CA, February, 1998.

E. J. Amis, B. D. Ermi, and Y. Zhang, Low-Charge Density Polyelectrolytes in Good Solvent, American Physical Society National Meeting, Los Angeles, CA, March, 1998.

B. D. Ermi, Development of Measurement Tools to Characterize Polyelectrolyte Solutions and Polymer Films, National Starch and Chemical Company, Bridgewater, NJ, August, 1998.

E. J. Amis, B. D. Ermi, and Y. Zhang, Unveiling the Puzzles of Polyelectrolytes with Small Angle Neutron Scattering, Multicomponent Polymers and Polyelectrolytes, Closing Symposium of ERATO Hashimoto Phasing Project, Kyoto, Japan, September, 1998.

B. D. Ermi, Development of Measurement Tools to Characterize Polyelectrolyte Solutions and Polymer Films, Kodak, Rochester, NY, September, 1998.

E. J. Amis, Unveiling Polyelectrolytes with Small Angle Neutron Scattering, Center for Interfacial Engineering Industrial Workshop, University of Minnesota, Minneapolis, MN, September, 1998.

Polymer Blends and Processing Program Outreach

E. J. Amis,