Development and characterization of poly(vinylidene fluoride)–poly(acrylic acid) pore-filled pH-sensitive membranes

Pore-filled pH-sensitive membranes were developed by in situ cross-linking poly(acrylic acid) inside poly(vinylidene fluoride) hydrophobic microporous substrate membranes. The incorporation of the poly(acrylic acid) gel, expressed as membrane mass gain, increased with the monomer concentration in polymerization solution and the amount of cross-linking degree. By the incorporation of the poly(acrylic acid) gel, the membrane performance was substantially altered. These membranes demonstrated a rapid and reversible response of flux to environmental pH as the pH was changed between 2.5 and 7.4. This pH-valve effect was observed at pH between 3.5 and 5.5. The membrane pure water permeability and valve ratio, as a function of environmental pH, were characterized by pressure-driven experiments in terms of the membrane mass gain and the cross-linking degree. The effects of the mass gain and the cross-linking degree were different at pH acidic and neutral. The overall effect was that as the mass gain decreased or the cross-linking degree increased, the pure water permeability increased. A high valve ratio was obtained when the mass gain was low and the cross-linking degree was high.