The Role of Grafting Mechanism on the Self-Assembly and Properties of Polymer Nanocomposites

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NON-TECHNICAL SUMMARY: The addition of inorganic nanoparticles (NPs) to a polymer (i.e. a plastic material) can result in hybrid materials with highly improved properties. A classic example is that, while rubber (as e.g. in an eraser) has extremely poor wear resistance, the addition of silica nanoparticles causes the wear resistance to go up so much that a car can drive with tires that last over 50,000 miles. While such property improvements are what drive developments in the field of polymer nanocomposites, the inherent problem is that the nanoparticles are chemically so different from the polymer (a hydrocarbon material) and thus have a strong tendency to separate from each other akin to a water-oil suspension. Thus, the desirable, favorable property improvements that can only be realized by the intimate mixing of the polymer and the NPs become hard to realize on a routine basis. The work here proposes to remedy this problem by chemically grafting polymer chains onto the NPs so that the inorganic particle surface can be "shielded" from the polymer, thus allowing miscibility to be obtained. In particular, the work focuses on two strategies for this grafting: either grafting fully formed chains to the surfaces, or growing the chains piece-by-piece from the surface. Which of these strategies allows better control over particle-polymer miscibility and therefore improve properties the most is the focus of this research. In addition to this technical emphasis, the proposed work will also stress the broad, interdisciplinary education of students and the recruitment and retention of women and minority students into STEM programs by attracting high-school and undergraduate students into engineering research activities in the PI's laboratory.TECHNICAL SUMMARY: The focus of this proposal is on the self-assembly of polymer-grafted nanoparticles (NPs) in a polymer matrix with the goal of impacting the behavior of the resulting hybrid (or composite) material. This physical situation has relevance to improved performance in, for example, rubber tires and epoxies (which are used in electronic packaging and computer chip applications). This underpinning question will be studied through the exploration of three test-beds by judiciously combining theory and experiments. In particular, emphasis will be placed on role of the mechanism by which chains are grafted onto NP surfaces on the final material properties, i.e., whether the chains are preformed and attached to the surface or if the chains are grown link-by-link from the surface. It is expected that the former mechanism will yield a more uniform polymer coverage on the NP surface. The consequence of these differences in surface coverage on the assemblies formed and the resulting properties is the ultimate focus of this work. These research activities are coupled to extensive education and outreach activities. A major focus will be to recruit underrepresented students (both women and minorities) at both the undergraduate and graduate levels. It is planned to grow both the current summer high-school research program, and also the research-experiences-for-undergraduates program during the schoolyear, with the goal of recruiting (and hopefully retaining) women and minorities into STEM efforts.