Poly (N-isopropylacrylamide) grafted temperature responsive PET membranes: An ultrafast method for membrane processing using KrF excimer laser at 248 nm

Abstract

Temperature responsive membranes have garnered a lot of interest, recently, in different applications. A two-step novel method to fabricate temperature responsive polyethylene terephthalate (PET) – poly(N-isopropylacrylamide) (PNIPAM) pore-filled membranes using a 248 nm KrF excimer laser, is reported here. PET films can be selectively ablated in first step to obtain porous support membranes having highly ordered, regular, and well-defined pores over a range of pore sizes. The support membranes can then be pore grafted with PNIPAM hydrogel using the same pulsed excimer laser using a bottom-up approach. The grafting density of PNIPAM in the pores can be tuned by appropriately selecting the laser parameters, and water permeabilities ranging on over 6 orders, at room temperature, can be easily achieved within few seconds of grafting. The water permeabilities increase above the lower solution critical temperature (LCST) of PNIPAM as attributed to increase in effective pore size due to network deswelling inside the pores. The hydrogel network gets strongly grafted to the pore walls and remains mechanically stable inside the pores under the applied pressures. Diffusive transport of a small molecule is studied to evaluate membrane performance as temperature responsive barrier for controlled transport of solutes. The grafting is quantifiable by ATR-FTIR studies and the results can be correlated with chain growth in pulsed laser polymerization. The results establish our method as an efficient, fast, and economical method to fabricate thermo-responsive membranes.