Determination of the Chi Parameter for Polymer Blends from Molecular Simulations

The χ parameter introduced in the Flory-Huggins theory, which widely governs the phase behavior of polymer blends, is generally obtained from scattering experiments or by fitting to experimental data.  Despite its wide usage, techniques for predicting χ from the structure of polymer blends are not well established.

In this work, we focus on applying molecular simulations to estimate the χ parameter for two polymer blend systems.  The blends studied are: polyisobutylene (PIB)/polybutadiene (PBD) and polyethylene (PE)/isotactic polypropylene (iPP).  We use molecular dynamics simulation in conjunction with the integral equation theory formalism proposed by Schweizer & Curro [Journal of Chemical Physics, 91, 5059 (1989)] to determine the χ parameter for these systems.  The χ parameter results are explained in terms of the molecular structure of these polymeric systems. Simulation results are also compared with the experimental data that are available in the literature.