Solvent transport model for polyamide nanofilm membranes based on accurate Hansen solubility parameters

Polyamide (PA) nanofilm membranes for solvent filtration are widely used in various industries. However, reliable models that can describe solvent transport in PA membranes have yet to be developed owing to measurement challenges associated with the highly irregular, ultrathin, and crosslinked PA structure which hampers the accurate estimation of solvent−membrane affinity. In this study, we determined the Hansen solubility parameters (HSPs) of crosslinked PA membranes by quantifying the swelling degrees of a molecular layer-by-layer-assembled, model PA nanofilm in various solvents via in-situ atomic force microscopy. The newly determined HSPs of the PA layer, in combination with free volume and Flory–Huggins solution theories, were incorporated into the solution-diffusion model. Our refined solution-diffusion model accurately predicted the permeance of 16 different solvents by faithfully capturing the characteristics of solvent−membrane affinity. Our study reveals practical and fundamental insights into solvent transport in PA membranes along with providing robust tools for characterizing nanofilm properties.