Spectroscopic study on water diffusion in aromatic polyamide thin film

A clear understanding of water diffusion mechanism is crucial for the design of efficient thin film composite (TFC) membranes for reverse osmosis. In this work, water absorption and desorption processes in poly(metaphenylene trimesamide) (MPTA), the active layer of TFC membranes, have been investigated by FTIR. Three different states of water molecules in the film were identified. The spectral data were assessed using 2D correlation analysis, and the sequence of the interactions in the absorption and desorption processes between water and the polymer matrix was determined. The moderately strong bound water hydrogen bonded with –Cdouble bond; length as m-dashO and –NH– occurs first. Then water diffuses into free volume (microvoids), exhibiting weak hydrogen bonding interactions, as well as forms strong hydrogen bonds between the polyamide and water molecules. The process of water desorption is just the opposite in terms of the interaction sequence. Furthermore, it was found that a higher carboxyl content in the MPTA film results in a higher water flux.