Effect of PET support membrane thickness on water permeation behavior of thermally responsive PNIPAM-g-PET membranes

Abstract

A KrF excimer laser was used at 248 nm wavelength to fabricate support membranes and the final PNIPAM pore-filled thermally responsive PET membranes of four different thicknesses (50, 75, 100, 125 μm). The surface and cross-sectional morphologies of the ablated support membranes were elucidated using optical microscopy and micro-CT. Proper combinations of laser operational parameters (energy fluence, number of pulses, pulse frequency) and mesh size were determined for each thickness membrane based on energy required for perforation, average pore size and morphological observations.Temperature responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogel was grafted in membrane pores through pulsed laser polymerization (PLP) at 3 progressive grafting density values. Four thicknesses membranes of 4 grafting conditions (1 ungrafted and 3 grafted) were characterized using water permeation test. Permeation behavior and thermal response were found for all 4 thicknesses of membranes at grafted state, and the permeation results displayed a decreasing trend in permeability coefficient with increasing thickness, while thermal response displayed an increasing trend with increasing thickness at higher grafting density state. Scanning Electron Microscopy (SEM) was utilized to characterize the surface and pore grafting phenomena on membranes of different thicknesses under different grafting conditions. Our results indicate that the film thickness has little or no effect on kinetics of PLP for given laser operation parameters. Thus, our results reveal that similar crosslink structure is obtained in PNIPAM grafted in the pores of different thickness support membranes when using the same PLP conditions.