Multiscale modeling and computer simulation of polyhedral oligomeric silsesquioxane assemblies.

Self-assembly offers a promising strategy for manipulating the bottom-up assembly of nanometer-scale objects into useful structures for many diverse applications. Polyhedral oligomeric silsesquioxane (POSS) molecules are nanoscale building blocks with immense potential for constructing hybrid organic/inorganic materials with superior physical properties. The silicon corners of the inorganic nanocubes can be functionalized with a variety of organic tethers to precisely tailor assembly of the molecules into specific structures. To successfully control fabrication of POSS-based materials requires an understanding of the atomic- and nanoscale processes that occur during the assembly process. In conjunction with ongoing experiments, computer simulations and theory can provide fundamental insight into the self-assembly process, and are valuable tools for identifying and efficiently mapping the vast parameter space of complex POSS/polymer assemblies. The objective of this dissertation is to elucidate the self-assembly properties of polymer-tethered POSS at large length (∼100 nanometers) and time (∼10--100 nanoseconds) scales. These length and time scales are often difficult to assess experimentally. Simulation studies of self-assembly in these regimes require sufficiently large numbers of molecules, and coarse-grained mesoscale models have been developed based on electronic structure calculations and all-atom simulations of small numbers of molecules to reduce overall computation time. Model molecules are initially developed that capture the essential features of connectivity and interaction specificity of mono- and tetratethered POSS nanoparticles functionalized with block copolymer and homopolymer chains. Simulations of these model molecules are conducted over wide ranges of temperature and concentration to probe the influence of tether chemical composition, molecular weight, and number on self-assembly. The tethered POSS systems are predicted to exhibit several of the same morphologies as their conventional flexible coil block copolymer and surfactant analogues. However, the POSS nanoparticle imparts unique features to the resulting structures. To more faithfully capture self-assembly in POSS systems, a coarse-grained model of nonyl-tethered POSS dissolved in hexane is developed that directly corresponds to its explicit atom counterpart. Solvent-mediated effective potentials that capture certain structural features in the all-atom systems are derived using numerical procedures. Similar local intermolecular packings of POSS molecules are found in both the coarse-grained and corresponding all-atom simulations.PhDApplied SciencesChemical engineeringMolecular physicsPhysical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125627/2/3208433.pd