Preparation and characterization of pH memorizable charged gel membranes

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We describe the design and preparation of a novel pH-responsive charged membrane whose charge density has two values when it is immersed into low-pH and high-pH solutions, and can retain the values after immersing it into a salt solution of pH=5.5. A pH-memorizable amphotelic gel membrane was prepared by casting an acid solution of a mixture of poly(allylamine) and poly(vinyl alcohol) which contains 1 mol% of acrylic acid as copolymer component, and by crosslinking it in a glutaraldehyde solution^3. We also make a pH-memorizable composite membrane (PAP membrane). This membrane has a sandwich-like structure of a pH-memorizable layer and two positively-charged layers. The membrane was treated with two solutions of pH 1 and 13. After the treatments, the membrane potential was measured KC1 solutions of pH=5.5 at some time intervals. Ionic permeation through the membrane was also measured in a dialysis system consisting of the membrane and 0.01N NaNO_3 and 0.01N KC1 solutions. The catoin concentration change was measured by an ion selective electrode. The membrane potential shows that the potential after pH 1 and pH 13 treatments are -30mV and 30mV, respectively, and the values are almost constant for more than 170h in a salt solution of pH=5.5. This means that the membrane can "memorize" the pH state of the treatment solution even in a salt solution of pH=5.5. The permeability of Cl^- ion through the PAP membrane after the low-pH treatment was about 800 times larger than that of K^+ ion after the high-pH treatment. The membrane maintains the high-permeability of anions even in the solution of pH=5.5. The function of the membrane can be applied to ionic devices such as chemical valves in a chemical chips.