Modified Free-Volume Theory for Solvent Diffusion Considering Hydrogen Bonds: Application to poly(amic acid) Solution

The diffusivity of solvents in polymer solutions is crucial for thin film drying and is influenced by the interactions between the polymer and the solvent. This study examines the impact of hydrogen bonding between the polymer and solvent on the self-diffusion coefficient of solvents in a poly(amic acid) (PAA) solution of dimethylacetamide. A modified free-volume model (HBFV model) was developed, incorporating hydrogen bonds. It assumes that some solvent molecules form hydrogen bonds with the polymer, reducing their mobility and free volume. Molecular dynamics simulations analyzed the fraction of free and hydrogen-bonded solvent and calculated the self-diffusion coefficient of the solvent, validating the HBFV model. Although further investigation into the polymer free volume is needed, this study suggests that hydrogen bonding should be considered in free volume models for PAA solutions. The HBFV model enhances the applicability of the free-volume theory to systems with hydrogen bonds.