Poly(4-vinylpyridine-co-styrene) membranes do not show facilitated transport

Membranes of a copolymer of vinylpyridine and styrene are more permeable to hydrogen chloride dissolved in water than to other dissolved salts. The hydrogen chloride flux varies linearly with the hydrogen chloride concentration difference across the membrane, which is inconsistent with facilitated diffusion. The membrane apparently operates by a diffusion-solubility mechanism, with a diffusion coefficient around 2.2 × 10^-10cm²/sec and a partition coefficient of 450. Earlier claims of facilitated diffusion in this solid membrane probably result from artifacts like lag times and like chemical degradation of the membrane, though they may also result from relaxation of copolymer chains.