Mathematical model for the formation of thin-film composite membranes by interfacial polymerization: Porous and dense films

A general model for the formation of thin-film composite membranes, that co nsiders both diffusion- and reaction-controlled interfacial polymerization, under non-steady-state conditions, has been developed. Special models for either diffusion-controlled or reaction-controlled interfacial polymerizati on with steady- and non-steady-state conditions have been obtained by simpl ification; these agree with similar models, where available, in the literat ure. The porosity of the thin film is dependent on the amount of water that diffuses with the aqueous monomer into the formed film. The analytical sol ution for the model is consistent with the effect of diamine concentration and successfully predicts it for a polysulfonamide composite membrane fabri cated from 1,2-ethanediamine and a disulfonyl chloride. The model allows si mulation of various factors that affect thin-film formation, particularly f or those factors that are difficult to measure experimentally. This work si gnificantly extends existing theories and provides an important guide for e ffective control of the thickness of the surface barrier layer of thin-film composite membranes prepared by interfacial polymerization.