Effects of coagulant pH and ion strength on the dehydration and self-assembly of poly(N, N-dimethylamino-2-ethyl methacrylate) chains in the preparation of stimuli-responsive polyethersulfone blend membranes

Amphiphilic triblock copolymer poly(N, N-dimethylamino-2-ethyl methacrylate)-block-polyethersulfone-block-poly(N, N-dimethylamino-2-ethyl methacrylate) (pDMAEMA-b-PES-b-pDMAEMA) was used as an additive for the PES blend membranes that were fabricated through a non-solvent induced phase separation method. The pH and ion strengths of coagulant baths were adjusted and the as-prepared membranes prepared from these solvents were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR-ATR) and nuclear magnetic resonance (H-1 NMR). The results from XPS and H-1 NMR showed that the concentration and wettability of pDMAEMA on surface were dependent obviously on the non-solvents applied, demonstrating that the pDMAEMA in membranes displayed conformations that were adaptive to the coagulant bath by a controlled hydration/dehydration or protonation/deprotonation. These in-situ marked conformation transitions were reserved well on the as-prepared membranes and they were readily inspected by the contact angle measurement and XPS. The pH sensitivity of blend membranes was finally determined, and it was found that membranes prepared in salt and basic solutions generally showed much stronger pH sensitivity. The conclusions shown in this work will not only assist us to better understand the self assembly of pDMAEMA in membrane forming process but also provide a guide to prepare gating membranes with higher sensitivity. (C) 2014 Elsevier B.V. All rights reserved,