Hydrophilic molecular sieve surface layer formation in hydrophobic poly(1-trimethylsilyl-1-propyne) membranes

Abstract

The transport properties of benzene vapor, water vapor, and nitrogen gas were systematically investigated for vacuum-ultraviolet (VUV)-irradiated highly gas and vapor-permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) membranes by a xenon excimer lamp at 172nm. The photon was completely absorbed by the surface membrane, and the VUV irradiation did not depend on the color center and the bulk structure of the PTMSP membrane. Moreover, the two-step surface chemical structure change of the PTMSP membrane from the highly hydrophilic C=O bond-rich surface layer to the low hydrophilic SiO2-rich surface layer was observed after VUV irradiation, in contrast to the effect on general polymer membranes. The two-step surface photooxidation and scission reaction of PTMSP membranes was likewise discovered. The surface-modified layer exhibited gas barrier properties for benzene vapor and nitrogen gas, but not for water vapor, because the benzene vapor and nitrogen permeability decreased as the VUV-irradiation time increased. This gas and vapor permeability reduction strongly depended on the molecular size, whereas the water vapor permeability did not depend on the surface hydrophilicity. This hydrophilic surface layer possessed molecular sieve properties. Thus, the PTMSP membrane in this study was changed by VUV irradiation from a benzene vapor-permselective non-molecular sieve to a water vapor-permselective molecular sieve.