Chemical valves based on poly(4-vinylpyridine)-filled microporous membranes

Microporous membranes containing poly(4-vinylpyridine) anchored within the pores exhibit very large chemical valve effects with pressure-driven permea bility changing by more than three orders of magnitude as a function of pH. The factors affecting the magnitude of this valve have been examined with a series of well characterized, poly(4-vinylpyridine)-modified, microporous polypropylene membranes. The permeability of these membranes to HCl/H2O at different pHs was measured as a function of pore size of the starting base membrane and the amount of poly(4-vinylpyridine) anchored within the pores . An analysis of these results shows that the magnitude of the chemical val ve is largely determined by the permeability of the membranes in their open -valve states, i.e., high pH. While the magnitude of the chemical valve eff ect exhibited by the membranes varied, the pH at which the valve closed was in each case found to be similar and independent of pore size of the start ing membrane or amount of poly(4-vinylpyridine) anchored within the pores. The permeability of the membranes at low pH (when the anchored poly(4-vinyl pyridine) is ionized) was examined using two existing models of hydrodynami c permeability, namely, the pressure-driven flow through a right-cylinder p ore partly obscured by a graft layer of a hydrodynamic thickness L-H (brush model) and the hydrodynamic flow through supported hydrogels (pore-filled model). The theory of polyelectrolytes in the semi-dilute region was used t o estimate the chain parameters of the incorporated polyelectrolyte. The re sults obtained show that the applicability of each model depends on the por e size of the substrate membranes and the molecular weight of the polyelect rolyte. (C) 1999 Elsevier Science B.V. All rights reserved.