Collaborative Research: Self-Assembly of Polymer Grafted Nanoparticles

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Intellectual Merit: The focus of this proposal is novel materials created by isotropically grafting inorganic nanoparticles with organic polymers. Since the inorganic nanoparticles and organic polymers typically dislike each other, these hybrid particles behave like nanoparticle amphiphiles. By analogy to amphiphiles, these hybrid particles can self assemble into a range of superstructures of immediate relevance to many applications in the physical and biological sciences. Preliminary calculations suggest that this self assembly reflects a balance between the energy gain when particle scores approach versus the entropy loss of distorting the grafted polymers. The PIs plan to consider this issue theoretically and begin by delineating regions of parameter space where these self assembled structures are formed, and where they are equilibrium rather than temporally evolving structures amenable to kinetic control. Looking ahead, we ask how more complicated architectures, such as particles grafted with block copolymers might behave. This question is inspired by the large zoology of structures that have been predicted and obtained from triblock copolymers. The PIs also extend these ideas to other nanoparticle shapes, e.g., nanorods and nanosheets, and examine what shapes of nanoparticle assemblies may arise. Again, inspired by a broad range of experimental activities on block copolymers, the PIs query the role of external fields (e.g., flow, electric, magnetic) in directing the superstructures that form. The overarching goal is to a prior design isotropically decorated nanoparticles that can spontaneously assemble into progressively more complex superstructures. While these questions are of import from a fundamental viewpoint, they will be of particular practical interest since they provide unique means of controlling the global nanoparticle dispersion state, and hence the macroscopic properties, of polymer nanocomposites. The PIs propose a collaborative effort between two PIs, who will combine computer simulations and mean-field theory to tackle fundamental issues underpinning our nascent understanding of self-assembly (and directed assembly) of nanoparticle amphiphiles. The PIs have collaborated actively for over twenty years, and the PIs bring separate but complementary skill sets to the proposed research. The geographical proximity, and shared graduate students, also strongly facilitate this research and emphasizes the synergistic nature of the activities proposed. Broader Impact: The ability of decorated nanoparticles to self assemble into superstructures of arbitrary complexity, and the ability to direct this assembly process through the use of external fields, could fundamentally alter our ability to design nanoparticle assemblies (and hence polymer nanocomposites) with desired macroscale properties. Apart from these research activities, the PIs shall continue to develop REU programs targeting underrepresented minorities. The PIs shall utilize the fact that FAMU, a partner school, is a historically black school, and use this to recruit undergraduate students with the goal of retaining them in the sciences.