Molecular dynamics exploration of the barrier properties of small gas molecules in the semicrystalline parylene C

Poly(chloro-<i>p</i>-xylylene) (parylene C) is recognized for its outstanding chemical resistance, high thermal stability, biocompatibility, and superior permeability barrier properties. This material predominantly exists in a semicrystalline state. Despite its significance, theoretical studies simulating the semicrystalline parylene C system are scarce. This study aims to elucidate the relationship between the semicrystalline structures and the barrier properties of parylene C through a molecular dynamics approach. Semicrystalline parylene C with 10-50% aligned regions were constructed, which exhibited a degree of crystallinity ranging from 17% to 44%. We discovered that increased aligned chains could significantly alter the material's structure and morphology. These changes could further lead to variations in the density, fractional free volume, and pore size distribution of parylene C, thus affecting its glass transition temperature, permeability barrier and mechanical properties. Additionally, the relative values of gas permeability coefficients closely match experimental data. The insights into the structure-property relationship presented in this work could offer valuable guidance for developing functionalized and structured parylene C as coating materials.