pH-Responsive Permeation in Packed Layers of Polyacrylic Acid-Coated Alumina Particles

A pH-responsive permeation system based on a packed layer of polyacrylic acid (PAA)-coated alumina particles is reported. gamma-Alumina particles coated with PAA (M-w= 25,000) were synthesized using a silane coupling agent and polymerization agent. The permeation of 1.0 x10(-2) mol L-1 aqueous solutions through packed layers of the PAA-coated particles decreased in the following order: HCI > CH3COOH > pure water > CH3COONa >NaOH. The increased average specific resistance of the packed particle layer with increasing solution pH was ascribed to decreased interparticle spacing due to electrostatic repulsion of the negatively charged PAA chains upon deprotonation of the carboxyl groups at high pH values. Thus, packed layers of PAA-coated alumina particles are a simple, promising, and practical system for pH-dependent permeation.