Collaborative Research: Measurements of Yield Strength and Local Viscoelastic Properties Using Nanoparticle Embedment Methods

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The proposed work expands a novel nanosphere embedment experiment to the measure of the yield behavior of surfaces. The method also promises a novel, high spatial resolution method to map the surface mechanical/viscoelastic properties of polymeric and composite materials. The work builds on CMMI supported work in which it was found that nanoparticles smaller than a certain size sink into the surface and become fully engulfed by the polymer. Analysis suggests that the nanoparticles are fully engulfed only when the yield strength of the polymer surface is exceeded, which opens a route to measure the surface yield strength, as well as other properties at depths on the order of 20 nm. If successful, it will also lead to a technique to provide a surface property map of mechanical, including modulus, yield strength, and viscoelastic properties of polymer surfaces using embedment of a monolayer of clustered nanoparticles. The work also involves numerical analysis of the embedment process to include appropriate elastic-plastic, viscoplastic or viscoelastic constitutive models to extract nonlinear material properties. By its interdisciplinary nature, the project provides a rare training opportunity for students in both chemical engineering and mechanical engineering to step into research in the thermo-mechanical behavior of polymers at the nanoscale. In addition, it is a collaborative project in which the graduate students will have the opportunity to interact with students from another institution and work with them. Part of the work in this project will be divided into smaller projects for use in term projects in courses such as viscoelasticity and polymer physics offered by the PIs in this project. All significant results will be published in journals to disseminate the findings. It is anticipated that the graduate students working on the project will present their findings at national/international conferences.