Impacts of reaction and curing conditions on polyamide composite reverse osmosis membrane properties

Here we report on the impacts of organic solvent properties, reaction conditions, and curing conditions on polyamide composite reverse osmosis membrane separation performance, film structure, and interfacial properties. We provide direct experimental evidence that: (1) MPD diffusivity in the organic phase governs MPD–TMC thin film water permeability, (2) MPD diffusivity and solubility influence MPD–TMC thin film crosslinking in competing ways, (3) water permeability correlates most strongly with MPD–TMC film structure (i.e., crosslinking), and (4) salt rejection correlates most strongly with MPD–TMC film thickness and morphology. Overall, higher flux membranes with good salt rejection appear to comprise thinner, more heavily crosslinked film structures. Such high performance RO membranes are obtained by (1) selecting high surface tension, low viscosity solvents, (2) controlling protonation of MPD and hydrolysis of TMC during interfacial polymerization, and (3) optimizing curing temperature and time based on organic solvent volatility. Finally, although more research is necessary, our results suggest the rugose morphology and relative hydrophobicity of high performance MPD–TMC membranes might enhance concentration polarization and exacerbate surface fouling.