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Numerical Study of Polymer-Silica Nanocomposites :Molecular Weight Effect on Their Mechanical Properties

Thomas R. Roussel, Joshua Moore, and Keith Gubbins. North Carolina State University, Engineering Building I, Box 7905, Raleigh, NC 27695-7905

Highly ordered mesoporous polymer-silica nanocomposites have been synthesized by Liu et al (JACS 2006) using a triconstituent evaporation-induced self-assembly method. A Pluronic triblock copolymer (F127) was used as a template. Soluble resol polymer and prehydrolyzed TEOS (tetraethyl orthosilicate) are, respectively, used as organic and inorganic precursors, templated by the hexagonally distributed cylindrical micelles. It has been proposed that ordered mesoporous nanocomposites have “reinforced concrete”-structured frameworks with interpenetrating networks. The presence of silica in nanocomposites drastically inhibits framework shrinkage during the micelle removal by calcination, resulting in highly ordered large-pore mesoporous carbon-silica nanocomposites. The pore size is varied as a function of the surfactant molecular weight, polymerization degree of organic precursor, and the relative precursor ratio (Si/C).

For a better understanding of such materials, we perform Monte Carlo simulations on several bulk atomic structures. First, we built a united atom coarse grained model of resol and silica. The precursors interact weakly with each other and can form chemical bounds independently. We explore, numerically, the structural properties of the nanocomposite by adjusting the initial mass ratios of silica to resol. The degree of the polymerization is adjusted by decreasing the volume of the simulation box at different rates, corresponding to a fictitious evaporation of the solvent. We show how mechanical properties are reinforced as a function of the molecular weight of the polymer (resol). This preliminary study is the first step to investigate the mechanical properties of the nanocomposite templated by micelles.