CAREER: Resolving and mapping of nanoscale heterogeneities in polymer gels and determination of their impact on properties.

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Non-Technical Summary:Polymer hydrogels are jelly-like materials that consist primarily of water, and are held together by a sparse mesh of long molecules within the liquid. Hydrogels are ubiquitous, finding use in medical materials such as contact lenses, energy materials such as battery membranes, separation matrices for the chemical industry, commodities such as diapers, etc. These materials have been known for many decades to be non-uniform on a very small (nanometer) scale. This project seeks to reveal the nature of these non-uniformities and explore their relation to variations in performance. It will do so by utilizing a number of new types of super-resolution microscopy techniques together with complementary materials structure-property characterization approaches. The educational component leverages the research program as a platform to inspire the next generation of scientists and engineers. The scope includes: (a) outreach to underrepresented groups in STEM through creation of hands-on learning activities, videos and mentorship of K-12 students via an online learning portal; (b) expansion of polymer content and development of innovative curricula using evidence-based approaches such as primary literature in the classroom and student teaching in the context of service learning; and (c) mentoring through undergraduate and graduate polymer science research.Technical Summary:This work will integrate research, teaching, outreach and mentoring around elucidating the impact of uncontrolled nanoscale heterogeneities on the structure-property relationships of polymer gels. The objective is to map nanoscale variations in crosslink density of gels in real space and quantify the consequent non-affine deformation. These fundamental morphological studies will establish the contributions of network spatial heterogeneities to deviations from the predictions of classic theories of elasticity and reptation. The timeliness of the proposal draws on the recent ability of optical superresolution microscopies to non-destructively image the nanostructure of solvent-swollen polymer systems. The proposed work will answer an important scientific question -- what is the nanoscale structure of a gel -- and thus offer potential impact to a number of industries.