Preparation of Patterned Isopore Poly(urethane acrylate) and Microporous Poly(vinylidene fluoride) Membranes by Soft Lithography and Their Application to Water Treatment

Abstract

Membrane filtration process is widely used for water and wastewater treatments because of numerous advantages it offers. Critical issues in membrane processes are membrane fouling as well as broad pore size distribution. In this study, patterned isopore membrane with high fouling resistance was fabricated combining soft lithographic method with UV-curable polymer and the effect of pattern on particle deposition were elucidated. First, membrane with uniform pore size was fabricated using a soft-lithographic method. Due to the precisely controlled pore size by micro size patterns, the membrane presented narrow pore size distribution comparing with conventional membrane. Furthermore, because the UV-curable polyurethane acrylate with releasing agent which decreases surface energy of PUA was used as the membrane material, it gave rise to better anti-biofouling performance than materials of commercial isopore membrane such as polycarbonate. Second, a patterned isopore membrane with reverse-pyramid patterns was prepared from UV-curable polyurethane acrylate by the soft lithographic method and extent of particle deposition was investigated during microfiltration. The extent of particle deposition was dependent on not only the ratio of crossflow velocity to permeation velocity, but also the size of particles in the feed. Three dimensional modeling based on computational fluid dynamics was also conducted to predict the vortex formation and elucidate the anti-fouling mechanisms of reverse-pyramid patterned membranes. The vortex was in accordance with the trends of particle depositions during the microfiltration. Third, correlations between pattern shape and extent of particle deposition were investigated experimentally and were elucidated through three dimensional modeling. The extent of particle deposition on patterned membranes was dependent on both pattern shape and orientation. Three dimensional modeling predicted velocity profile and shear stress distribution on patterned membrane surface. The changes in hydraulic trait at each pattern affected particle deposition. In particular, maximum shear stress mostly governed the extent of particle depositions on the membrane surface.