Tutorial: Molecular Dynamics Simulations of Microstructure and Transport Phenomena in Glassy Polymers

Abstract

This synopsis illustrates the current possibilities and limitations of classical molecular dynamics (MD) simulations with respect to fully‐atomistic models of high‐performance glassy polymers such as polyimides. Realistic molecular models are potentially able to characterize the microstructures and transport mechanisms at the atomistic level, and thus complement experimental evidence. A hybrid pivot Monte Carlo – MD generation procedure, which allows for chain configurations characteristics of the equilibrium bulk melt to be created at the required temperature from single‐chain sampling under a local energy approximation, has been developed and validated for several different polymers. More recently, an original procedure, loosely based on the experimental solvent‐casting process, has been designed for creating membrane models. Direct applications include realistic bulk and membrane models of polyimide matrices, in an attempt to link macromolecular structure and dynamics to the transport mechanisms for a series of small penetrants. Polymers have first been studied in the pure bulk state in order to characterize the influence of the chemical structure on configurations, preferential interactions, void‐space morphologies or chain mobilities. In a second stage, gas or water molecules have been inserted into the pre‐prepared polymer matrices. Their diffusion and solubility properties have led to further studies on specific aspects of these models, such as the influence of simulation box size, or the presence of confined and freestanding interfaces on penetrant transport.