pH-Controlled Gating of a Porous Glass Filter by Surface Grafting of Polyelectrolyte Brushes

Poly(acrylic acid) (PAA, a polyelectrolyte brush) was grafted onto a porous glass filter in order to construct a pH-dependent system for the control of liquid permeation. The porous glass filter was treated with octadecyldimethyl( N,N -diethylamino)silane and subjected to glow-discharge treatment to facilitate graft polymerization of the acrylic acid. The surface was analyzed using measurement of the water contact angle, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The surface wettability of the glass filter decreased following silane-coupling treatment and increased following PAA grafting. Water permeation of the PAA-grafted glass filter was pH dependent. The permeation rate was high under low pH conditions and low under high pH conditions. A possible explanation for this permeation profile is that under low pH conditions protonated PAA chains shrink, thereby opening the pores of the filter, and that under high pH conditions dissociated PAA chains are extended to cover the pores. The permeation rate of a water/acetone mixture through the grafted glass filter was also pH dependent. The PAA-grafted glass filter was more stable for the mixture in comparison with a polymer filter.