Nanomorphogenesis of polyamide membranes by regulating activator-inhibitor diffusivity difference

Abstract

The use of nanofiltration (NF) membranes featuring crumpled polyamide layers with excellent permeance and selectivity is promising for efficient water reclamation. Although diffusion-driven instability has been regarded as the key mechanism for forming crumpled polyamide structures, in-depth analyses of the morphological and structural features of these membranes are still lacking. We used ammonium carboxymethylcellulose (CMC) and glutaraldehyde (GA) to crosslink and form a pH-responsive interlayer to manipulate the interfacial polymerization (IP) process and the microstructures of interlayered thin-film composite (TFNi) membranes. Experimental observations and molecular dynamics simulations indicate a transition point in the spatial patterns from irregular to regular polyamide nanostructures by tuning the diffusivity difference between the reactant monomers in the two immiscible phases during the IP process. Compared with irregularly crumpled TFNi membranes, regularly crumpled TFNi membranes exhibited polyamide layers with higher aspect ratios (i.e., height/lateral dimension), potentially offering an increased filtration area and sufficient nanovoids. TFNi membranes exhibited a 2.5-fold increase in permeance compared to pristine polyamide membranes, along with twice the selectivity (up to 87.2) for Cl−/SO42−. Our work provides molecular insights into the tuning of morphological features and membrane performance of crumpled polyamide membranes.