Zwitterionic Membrane via Nonsolvent Induced Phase Separation: A Computer Simulation Study

Dissipative particle dynamics (DPD) was adopted to study the nonsolvent induced phase separation (NIPS) process during a pH-responsive poly(ether sulfone) membrane preparation with a zwitterionic copolymer poly(ether sulfone)-block-polycarboxybetaine methacrylate (PES-b-PCBMA) as the blending additive. The membrane formation process and final morphology were analyzed. Simulation results show that the hydrophilic PCBMA segments enrich on the membrane surface by surface segregation and exhibit pH-responsive behavior, which is attributed to the deprotonation of the carboxylic acid group. With the polymer concentration increasing, both the shrinkage of the membrane and the flexibility of the system decrease, which also reduce the effect of surface segregation. By adjusting the blend ratio of PES-b-PCBMA with PES from 5% to 15%, the surface coverage of PCBMA segments on the membrane can be regulated. This work contributes to a better understanding on the mechanism of NIPS and can serve as a guide for the design of the polymer blend membrane.