Interfacially polymerized thin-film composite polyamide membrane: positron annihilation spectroscopic study, characterization and pervaporation performance

Abstract

To improve the pervaporation performance of polyamide membrane, thin-film composite (TFC) polyamide membranes were prepared through the interfacial polymerization between m-phenylenediamine (MPDA) or 1,3-phenylenediamine-4-sulfonic acid (MPDASA) and trimesoyl chloride (TMC) on the surface of the modified asymmetric polyacrylonitrile (mPAN) membrane and applied in the pervaporation separation of 70 weight % aqueous isopropanol solutions at 25 °C. The variations in the free volume and the thickness of the active polyamide layer of composite membrane were obtained by positron annihilation spectroscopy (PAS) experiments, in which a variable monoenergy slow-positron beam was used. FTIR-ATR spectroscopy, XPS, scanning electron microscopy, AFM and water contact angle measurements were applied to analyze chemical structures, surface elemental compositions, morphologies, surface roughness and hydrophilicity of the active polyamide layer of composite membrane. From the result of PAS experiments, the S parameter (corresponding to the free volume size and amount) and the thickness of the active polyamide MPDASA-TMC/mPAN layer were found to be lower than those of the active MPDA-TMC/mPAN layer. In the aqueous isopropanol solution dehydration, the MPDASA-TMC/mPAN membrane exhibited a higher permeation rate than but maintained the same water concentration in the permeate as did the MPDA-TMC/mPAN membrane. This is in good agreement with the analysis by PAS. The variations in the free volume and the thickness of the active polyamide layers of the composite membranes were obtained by positron annihilation spectroscopy (PAS) experiments, in which a variable monoenergy slow-positron beam was used. The data on Doppler broadening Sparameters vs annihilation radiation energy spectra showed that the active MPDASA-TMC layer of the composite membrane had a lower free volume and was thinner than the active MPDA-TMC layer. This result corresponded well with that from the pervaporation performance of TFC polyamide membranes.