In polyamide membranes for water purification, the degree of conversion between acid chlorides and amines dictates crosslink density, degree of swelling, and water and ion transport. In this talk, two measurements techniques for quantifying the concentration of the relevant functional groups (amides, free amines, free carboxylic acids) will be described and critically assessed. These measurement techniques are particularly suited for probing functional groups in ultrathin films (h &lt; 200 nm). The first technique involves substrate-overlayer attenuated total reflection IR spectroscopy (SO-ATR IR), where signal enhancement originates from constructive interferences of the evanescent wave within the film. Carboxylic acid concentration in ultrathin membranes was characterized by interpolating integrated absorbance values of the free acid band at 1718 cm-1 based on a calibration curve generated from interfacial polymerization samples of known acid content. The second technique involves the use of resonant soft x-ray reflectivity (RSoXR), where scattering contrast is enhanced for specific functional groups near an absorption edge. The optical constants for each functional group were calibrated using a series of reference films of known functional group concentrations, allowing functional group quantification in an unknown film. We then relate the functional group concentrations measured via SO-ATR IR and RSoXR to the transport properties (water and salt permeability) of the membranes.

Functional group quantification in polyamide membranes

255th National Meeting (2018)

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