Inter- and Intramolecular Effects on Conformation in Polymers and Liquid Crystals

The behavior of soft materials depends on molecular conformation, yet it is often infeasible to predict accurate structures in the bulk phase at low computational cost. Here, we examine polymer melts through the rotational isomeric state (RIS) approximation, where intramolecular effects dominate, and contrast them with liquid crystals, where intermolecular interactions govern conformation. We develop a tool to apply the RIS approximation to arbitrary polymer chemistries through fragmentation, generation of the underlying potential energy surfaces--using density functional theory or machine learned interatomic potentials--and then subsequent conditional sampling of dihedral pairs. By recovering ideal chain statistics and melt-phase observables, we reaffirm that the conformational landscape of polymer melts is governed predominantly by single-chain characteristics, leaving interchain interactions less dominant. This is compared to liquid crystals, where we optimize an existing classical forcefield and use machine learning based analysis to demonstrate that intermolecular packing effects drive conformational differences. These insights help us build models for systems governed by intramolecular interactions, while also acknowledging the challenges inherent to modeling partially ordered phases in chemically sensitive environments.