Anti-fouling behavior of micro-patterned PVDF membranes prepared via spray-assisted phase inversion: Influence of pattern shapes and flow configuration

Abstract

One of the key issues in membrane technology is to avoid fouling formed on the membrane surface. Patterned surfaces have been suggested as one of the ways to reduce fouling. In this report, both experimental and simulation studies were performed using membranes with rectangular and triangular patterns, synthesized via the recently developed s-NIPS method. A casting solution composition of 20 wt% PVDF, 6.7 wt% PVP and 1 wt% H2O in DMF was used to create homogeneous patterns. Well-patterned membranes showed 95–140% higher PWP attributed to the additional effective surface and change in intrinsic membrane morphology associated with the non-solvent spraying. Reduced particles deposition after 3 h continuous filtrations and delayed cake layer formation were observed as compared to the counterpart flat, un-patterned membrane. CFD analysis for different feed to pattern directions (θf) showed the local flow distribution near the patterned grooves. For θf = 90°, vortices in the upper part of the patterns could potentially reduce the particle depositions, while aggregates of foulants can be easily formed in vortices developed in the lower part of the pattern, leading to a favorable fouling formation. On the other hand, for θf = 0°, the flow gave rise to effective slip velocities near the patterned membrane surface, hence reducing the particle adhesion. This indicates the importance of flow characteristics as well as the stress distribution to reduce the fouling in the patterned membrane system. Higher inter-pattern distances, i.e., Rec2000_w and Tri2000_w, led to unfavorable BSA deposition. This combined effect of patterning and s-NIPS resulted in higher effective surface area, reduced fouling and increased membrane porosity which substantially increased the membrane permeance and anti-fouling potential. These results suggest promising application of patterned PVDF membranes prepared via spray modified-NIPS for filtration.