Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes

Abstract

Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane's salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a..