Modelling of the pore structure variation with pH for pore-filled pH-sensitive poly(vinylidene fluoride)–poly(acrylic acid) membranes

Pore structure variation as a function of pH was investigated for the pore-filled pH-sensitive poly(acrylic acid)-poly(vinylidene fluoride) membranes. The pore radius reduced drastically as the poly(acrylic acid) gel incorporated inside the nascent substrate, which is from 113 nm of nascent substrate to as low as 7.0 nm of pore-filled membranes at pH acidic. For the membranes, the pore radii at pH neutral estimated by the extend Nernst–Planck equation (2.76–4.20 nm) and by the Spiegler–Kedem model with the steric-hindrance pore model (3.4–4.1 nm) are close to each other and comparable with that calculated from the poly(acrylic acid) gel correlation length (1.79–2.93 nm). The calculated pore density at pH neutral (49–258 × 1014 m−2) is much higher than that at pH acidic (2.8–39.8 × 1014 m−2). The results are interpreted in terms of the gel structure in the pore-filled membranes.