Versatile Anisotropic Coarse-Grained Models for the Structure and Dynamics of Unentangled Poly(tetrafluoroethylene) Melt

We develop anisotropic coarse-grained (CG) models for unentangled poly(tetrafluoroethylene) (PTFE) melts to investigate their structural and dynamical properties at two CG levels, corresponding to six and eight CF2 groups per bead. Higher CG levels improve computational efficiency but face challenges, such as unphysical chain crossing due to reduced steric hindrance and weaker interactions. Additionally, the inherent chain stiffness of PTFE chains is evident. Analyses of the gyration tensor and asphericity indicate that structural anisotropy increases with CG levels. Therefore, we pursue a structure-based, bottom-up coarse-graining approach based on accurate all-atom (AA) simulations. Systematic probing of intermolecular interactions, internal conformations, and global chain dimensions reveals that our models effectively capture structural characteristics. Chain stiffness, such as the Kuhn length, agrees reasonably with AA simulations and experimental data. Furthermore, with appropriate scaling factors introduced, these CG models closely align with the atomistic counterpart in dynamics, including self-diffusivity and zero-shear viscosity. Assessments across molecular weights (48–192 carbons per chain) and temperatures (500 to 650 K) confirm the adaptability of these models. Utilizing the devised CG models, the computational efficiency is approximately accelerated by a factor of N2, where N is the number of CF2 groups per CG bead.