Preparation of pH-responsive polymer membranes by self-organization

Self-organizing blends of poly(vinylidene fluoride) (PVDF) and an amphiphilic comb polymer having a PVDF backbone and poly(methacrylic acid) (PMAA), side chains are examined as a means to prepare membranes with pH-responsive separation characteristics. X-ray photoelectron spectroscopy analysis of membranes prepared from these blends indicates substantial surface segregation of the comb polymer during the standard immersion precipitation process for membrane fabrication, such that a near-surface coverage of 29 wt.% PMAA is achieved on membranes containing 10 wt.% comb (5 wt.% PMAA). Fluorescence microscopy studies on membrane cross-sections further reveal surface expression of PMAA on internal pore channel surfaces throughout the membrane. Membranes cast from these blends exhibit a reversible, pH-dependent flux variation of over an order of magnitude as the feed solution pH is varied between 2 and 8. The pH-dependent conformational changes of the PMAA surface layer are confirmed by force microscopy. These results demonstrate that “smart”, environmentally responsive (ER) membranes can be prepared by immersion precipitation with no post-coagulation processing steps.