Control of silicate nanocomposite morphology in binary fluids: Coarse- grained molecular dynamics simulations
KL Anderson and A Sinsawat and RA Vaia and BL Farmer, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 43, 1014-1024 (2005).
In situ polymerization is the most successful technique for thermoplastics and thermosets for the preparation of well-dispersed polymer-layered silicate nanocomposites with desirable mechanical, thermal, and electrical properties. The efficiency of this approach depends significantly on the polarity of the monomer and curing agent and the intermolecular interactions at the silicate surface. To explore the intermolecular interactions that influence morphology development on the mesoseale, large-scale coarse-grained models comprising a coherent stack of platelets immersed in a sea of binary fluids (representing the monomer and curing agent) have been used under isothermal isobaric conditions. The beads in the mixtures differ in their relative affinity for the silicate sheets. The simulation results indicate that completely intercalated structures can be obtained by the simple adjustment of the relative concentration of the binary fluid mixture and the pressure experienced by the nanocomposite. The generation of internal pressures associated with intercalation within a microcanonical (constant particle-volume-temperature, NVT) simulation has an impact on the observed processes. The isobaric (constant particle-pressure- temperature, NPT) ensemble is believed to more effectively represent the actual nonequilibrium intercalation process. Partial intercalation occurs at low concentrations of the component most strongly attracted to the sheets. Under select conditions, a steady increase of intercalated fluid beads indicates the initial stages of the formation of an exfoliated. structure. Indeed, exfoliated structures have been observed in simulations of sheets with lower aspect ratios. A strong partitioning effect can be seen even for low concentrations of the attractive fluid. 02005 Wiley Periodicals, Inc.
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