Structure of Poly(dimethylsiloxane) Melts:  Theory, Simulation, and Experiment

Molecular dynamics simulations, integral equation theory, and wide-angle X-ray scattering experiments are used to study the structure of a poly(dimethylsiloxane) (PDMS) melt. Two different chain models are employed for the molecular dynamics: a united-atom class I potential and an explicit-atom class II potential. The effects of partial charges and attractions on the intermolecular pair correlation functions are studied for the united atom model. Good qualitative agreement between the polymer reference interaction site model (PRISM theory) and the simulations is found for the united atom model with charges and attractive dispersion interactions turned off. Simulation results for both the united-atom and explicit-atom models for the structure factor are in excellent agreement with the X-ray scattering measurements for high wavevector. However, the explicit-atom model gives significantly better agreement for low wavevector, particularly in the vicinity of the first peak.