The research performed at the Polymers
Division is responsible for providing standards, measurement methods,
and fundamental concepts of polymer science to assist those US industries
that produce or use synthetic polymers, plastics, and rubber in essential
parts of their business. Please also note the NIST
disclaimer.
Characterization and Measurement
Research focuses on ways to
characterize polymers for processibility, properties, and performance.
All areas of materials science today confront real systems and processes. We can, in many cases, no longer advance science by simply studying model systems that are idealized in dimension and function.We must comprehend complex realistic three-dimensional systems in terms of their structure, function, and dynamics over the size range from nanometers to millimeters. At NIST, we are uniquely positioned to make a major contribution to the development of measurement infrastructure through the synergism of advanced imaging and visualization techniques. By combining information from different techniques on the same sample and visualizing structure using interactive, immersive visualization techniques, scientists will gain new insights into the physics and materials science of complex systems.
Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a well-established method for determining the mass of macromolecules. This comes from the relatively simple relationship that exists between the instrument parameters (ion accelerating voltage, flight path length, and flight time) that are used to calculate ion mass. However, for polydisperse materials the relationship between the recorded ion intensity of a given oligomer and oligomers true abundance in the sample is an unsolved problem. The effect of the details of polymer chemical structure, MALDI sample preparation, and instrument parameters all affect the results in various ways. The lack of calibration of the ion intensity axis of the MALDI-TOF MS spectrum may lead to large uncertainties in quantifying the content of mixtures, whether the mixture is composed of different oligomeric species of the same polymer (molecular mass distribution), polymers of the same repeat unit but having different end groups, or polymers having different repeat units. NIST/industry workshops have established that quantification of MALDI-TOF MS would provide enormous benefits in applications ranging from basic polymer research to production quality control. Work at NIST involves a multifaceted attack on the characterization of the MALDI process and its relationship to signal intensity including:
Photolithography is the driving technology and key enabler for the fabrication of integrated circuits with continuously decreasing feature sizes. It is largely the successful fabrication of smaller structures that have fueled the continued performance increases in microprocessors.
Currently, state-of-the-art photolithography materials and processes can fabricate 100 nm features, but significant technical hurdles remain in making sub-100 nm features. These challenges include optics for new imaging radiation energies and the development of photoresists applicable at these wavelengths.
The goals of this project are to develop and apply our expertise in high-resolution metrology and polymer thin films to advance photoresist formulations and fabrication strategies.
We are developing an integrated program of fundamental studies correlated with resist performance metrics such as critical dimension (CD) and line-edge roughness (LER) that will have a broad industrial impact.
Precise measurements of critical dimensions and feature resolution are needed to evaluate the efficacy of new materials and processes, particularly for smaller feature sizes. Current microscopy-based techniques (AFM, SEM) are labor-intensive, time-consuming, limited in sampling area, and have difficulty measuring smaller, high aspect ratio, device features. Recently, light scatterometry has emerged as a prevalent metrology, however the technique is expected to experience reduced sensitivity as pattern size continues to shrink below sub-100 nm. In addition, visible light techniques are inherently limited in their capability to probe opaque materials such as in the limit of dense, high aspect-ratio features. A new high-resolution metrology is required to quantify critical dimensions and feature quality (line-edge roughness, LER, and sidewall roughness). The goal of this project is to develop a new X-ray based methodology to quickly, quantitatively, and non-destructively measure critical dimensions and feature resolution of nano-scale on production scale test samples.
Novel dielectric hybrid materials based on organic resins filled in the dielectric modifiers been identified by the industry as key materials for advancing miniaturization and functional performance of microwave electronics. The objective of this project is the development of broadband dielectric metrology for such materials and enable fundamental understanding of high frequency relaxation mechanisms in relation to structural and molecular attributes.
Provide structure and property information (composition, porosity, CTE, average pore size, moisture uptake, pore connectivity) of nanoporous low- k thin films
to SEMATECH, material suppliers and other microelectronic companies. Develop contrast- matching technique to provide an alternative method of wall
density measurement and new method of measuring wall heterogeneity.
The dental materials project currently has efforts in two fronts designed to enhance our fundamental understanding in 1) dental restorative composites and nanocomposites 2) biocompatible hydrogels for periodontal tissue regeneration. In the area of restorative composites, we focus on developing bioactive fillers, understanding their roles in remineralization, their properties as the fillers. Various methods to improve the dental composites, both traditional and bioactive fillers, through the use of additives, such as low molecular mass organogelators, various reactive and non-reactive silane-coupling agents, are also explored. In addition to dental restorable composites, we are expanding our efforts to include periodontal tissue regenerations. This is done in collaboration with ongoing tissue engineering research in the biomaterials group with the goal of understanding the relationships between various material properties and cell response.
Polymeric scaffolds form the basis for many tissue engineering approaches to restorative or regenerative medicine. The performance metrics for these devices are complex, and they present a host of characterization issues that need to be overcome for the field to advance. We are developing metrologies that address issues of mechanical performance, induction of tissue development, and inflammatory responses. These properties all depend sensitively on the chemistry and structure of the scaffolds and development of structure/property relationships for these devices is central to our approach. Mechanical performance is being characterized using video imaging and particle tracking to characterize local strain fields and bulk properties. To characterize tissue development, three-dimension, chemically specific imaging techniques are being established to follow cellular organization and matrix production in situ, and quantitative real-time polymerase chain reaction (QRT-PCR) techniques are being used to measure the response of inflammatory cells such as macrophages to materials.
Tissue engineered medical products (TEMPs) are radically changing the medical treatment of injury and disease. This new industry requires an unprecedented integration of materials science and biology, and an adequate measurement infrastructure must be established. This project sets forth to contribute a set of novel measurement methodologies for assessing cell-biomaterial interactions. Over time, the effort has evolved into four interwoven tools: material libraries, indicator cells and single cell metrology, high throughput screens, and statistical treatments of population distributions. Material libraries are being produced using gradient methodologies developed by the NIST Combinatorial Methods Center. This approach facilitates the rapid screening of a large material parameter space that includes: surface energy, crystallinity, roughness, topological patterns, compliance, and degradability. Indicator cells and single cell metrology complement the material libraries by enabling the rapid assessment of cell response. These fluorescence-based techniques range from simple staining protocols to more complicated strategies for GFP-related genetic engineering being developed by collaborators in CSTL. High throughput screens of cell-biomaterial interactions are being devised using an automated fluorescence microscope equipped to scan and correlate single cell metrics across a large material parameter space. Other methodologies for high throughput screens are also being considered. Finally, as high throughput screens generate larger data sets, statistical treatments of population distributions must be carefully examined. Through collaborations with ITL, the data output from high-throughput screens is being interfaced with statistical software to provide the most relevant, unbiased analyses possible.
Over the last decade, interest in polymeric materials containing dispersed inorganic nano-particles has skyrocketed due to the potential for significant advances in mechanical, thermal and flammability properties. Commercialization of these materials has thus far been slow due in part to the difficulties associated with the cost-effective dispersion of these particles into polymeric resins during processing. The goal of this project is to understand and quantitate the factors necessary to create well dispersed materials.
The goal of Quantification of Polymeric Flow is to bring quality measurement capabilities and philosophy into an industry that typically relies on crude techniques. Current efforts focus on two areas:
I. Development of Frustrated Total Internal Reflection for the in-situ measurement of coatings.
II. Measuring the response of confined polymeric emulsions to simple shear.
The goal of this project is to develop processing and measurement methods that will aid in micro- and nanoscale manufacturing, contributing to NISTs larger strategic focus on nanotechnology. Innovative nanometrology efforts include high-resolution microscopy of self-assembled materials and nanorheological measurements. Also being developed are new small-scale fluidic devices, capable of synthesis, processing and measurement of materials properties.
The NIST Combinatorial Methods Center (NCMC) was established in January 2002 to provide information and expertise on combinatorial methods to industrial and academic institutions interested in acquiring combi and high throughput materials research capabilities. The NCMC functions through two complimentary efforts: 1) An outreach program designed to gauge industrial needs in combi research and effectively disseminate data, instrument designs, best practices and protocols, and other information relevant to combi techniques. The crux of NCMC outreach is an industrial/government consortium, which has attracted 14 partners from the chemical and materials research sectors. 2) An exploratory research program designed to increase intra-NIST collaboration in combi methods development and establish combi expertise in new arenas of industrial interest. Current exploratory efforts in combi informatics and gradient techniques for nanotechnology will be incorporated into future formal projects.
The goal of this project is to develop methodologies and measurement techniques designed to rapidly assay material properties of polymers and formulations under numerous different experimental conditions. Towards this end, we have focused our efforts in three specific areas. First, combinatorial approaches have been applied to both the industry-standard peel test as well as the more recent JKR technique. These methods are being used to study polymer/polymer adhesion as well as polymer/metal and polymer/inorganic adhesion. Secondly, we have exploited a buckling instability in multilayer laminates to ascertain the modulus of thin polymer films. The modulus of a film can be calculated from the periodicity of the buckles, which can be determined at individual points across the sample by light scattering, thereby making it a high-throughput technique. Thirdly, we have applied combinatorial approaches to copper-grid tests, which allows crazing and fracture of polymer films to be studied as a function of film properties and thermal history. Each of these methodologies are designed both to increase awareness in how combinatorial approaches can be used in existing techniques as well as aide in knowledge generation in the areas of adhesion and mechanical properties.
The goal of this project is to develop high throughput methods to advance polymer formulations science through the fabrication of microscale instrumentation for measuring physical properties of complex mixtures. Tools and techniques for synthesis, mixing and measurement capabilities are being designed and implemented in robust fluidic modules that can ultimately be adapted to a range of formulative systems.
The dental materials project currently has efforts in two fronts designed to enhance our fundamental understanding in 1)