Modeling of PDMS - Silica Nanocomposites
J.S. Smith, G.D. Smith and O. Borodin
University of Utah, US
Keywords: nanocomposite, molecular dynamics, polymer simulation, quantum chemistry, polymers, modeling
A hydrogen bonding pathway between polydimethylsiloxane (PDMS) and hydroxyl groups on a silica surface was studied using quantum chemistry calculations of disiloxane and hexamethyldisiloxane molecules with small silica clusters. A newly developed classical force field for PDMS was used in atomistic molecular dynamics simulation studies of PDMS/silica nanocomposites to determine the effect of these interactions on the dynamics and structure of PDMS. A three nanometer silica particle (b-crystobalite) with (111) surface hydroxyl group density of 4.8 OH groups/nm2 was simulated in a PDMS melt in the temperature range of 300 to 500K. The density and structure of PDMS chains near the silica surface were strongly influenced by the hydrogen bonding interaction which is not properly represented in other current force fields. Residence time correlation analysis confirmed that PDMS oxygen silica surface hydrogen atom dynamics were consistent with polymer hydrogen bonding. The dynamics of backbone atoms in the PDMS chains are an order of magnitude slower than bulk polymer at the same temperature consistent with experimental findings. Results of this study are compared with simulation and experimental results on nanocomposite systems.
Nanotech 2004 Conference Technical Program Abstract