NIRT: Influence of Nanoscale Structure and Dynamics on the Deformation of Polymer Glass Nanocomposites

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ABSTRACT - 0506840U of Wisconsin MadisonEven though polymeric glasses are impressive engineering materials, there are considerable opportunities to improve their strength and failure properties. Recent evidence indicates that reinforcement of polymer glasses with nanoscale particles (i.e. nanocomposites) can produce materials with strength and failure properties that are substantially improved and, given current understanding, cannot be produced in any other manner. The systematic development of new glassy nanocomposites will require an intricate understanding of deformation processes on the nanoscale. We propose an integrated effort that utilizes experiments, simulations, and theory to develop the needed understanding. Experiments will be used to characterize both the macroscopic and microscopic deformation behavior of model PMMA/silica nanocomposites. Deformation-induced polymer mobility will be quantified for the first time in these materials. Experimental results will be compared with continuum, mesoscale, and microscopic theoretical approaches. Computer simulations will guide and check the theoretical developments. Key questions to be addressed include: What is the interaction between the intrinsic nanoscale heterogeneity of a polymer glass and the presence of a nanoparticle? For what size nanoparticles do continuum models of the polymer glass fail to describe the experimental behavior? What is the microscopic origin of deformation-induced mobility? What are the dynamics inside a fibril created by crazing? What is the relationship between mechanical and dynamic heterogeneity in polymer glasses? The computational demands of the proposed work are substantial and we will take full advantage of the emerging national cyber infrastructure, including the NSF supported Grid Laboratory of Wisconsin (GLOW). We anticipate that this work will have broad impact in at least two dimensions. New polymer glass nanocomposites are urgently needed to solve vexing manufacturing problems such as the weakness of nanoscale photoresist features created by advanced lithography. Our primary technical goal is to develop tools that, using a minimum of experimental input, can predict the deformation properties of glassy nanocomposites as a function of temperature, thermal history, strain rate, and deformation geometry. Additionally, the PIs will work with a University of Wisconsin-Madison program known as PEOPLE (Pre-college Enrichment Opportunity Program for Learning Excellence) to increase the likelihood that minority and low-income high school students matriculate to colleges and universities. The PIs and our coworkers will provide experiences that will help these students to become scientifically literate citizens and encourage them to consider careers in science and engineering; we will work with teachers of these students in our laboratories and in the development of instructional materials. The PEOPLE program has a proven track record of sending more than 90% of its participants to college.