Effect of the surface property of poly(tetrafluoroethylene) support on the mechanism of polyamide active layer formation by interfacial polymerization

The mechanism of polyamide formation by interfacial polymerization is important fundamental knowledge for understanding the properties of the polyamide active layer of thin-film composite (TFC) membranes. In this study, TFC membranes of polyamide using poly(tetrafluoroethylene) (PTFE) as the support were prepared by interfacial polymerization. The effect of the surface property of the PTFE membrane support on the mechanism of formation of the polyamide active layer was investigated. Characterization of polyamide–PTFE composite membranes was performed by attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. Positron annihilation spectroscopy was used to analyze the microstructural variation in the polyamide active layer. The growth of the polyamide film was affected by the surface property of the PTFE support. Positron annihilation lifetime spectroscopy (PALS) results showed that the densest structure was at the interface between the polyamide layer and the PTFE support for the polyamide–hydrophilic PTFE composite membrane system; however, the densest structure was at the top surface of the polyamide active layer for the polyamide–hydrophobic PTFE composite membrane system. The high electronegativity of the –CF2– groups on the PTFE support caused "quenching" and "inhibition" effects, resulting in a dramatic decrease in the o-Ps intensity.