Donnan Potential in Hydrogels of Poly(Methacrylic Acid) and its Potassium Salt

Donnan potentials have been measured in polyelectrolyte hydrogels gels of poly(methacr-ylic acid) and their potassium salts in water, using Ag/AgCl microelectrodes at 298 K. The Donnan potential varied from -80 to -40 mV as a function of gels’ cross-link density and the fraction of potassuim methacrylate monomer units. Negative values of the potential increase with the decrease in cross-link density of the gel. Gels with an increasing fraction of potassium methacrylate yield less negative values. The results are discussed from the viewpoint of the Donnan theory initially developed for membrane potential. The theory is qualitatively consistent with observed dependencies of the potential. However several quantitative differences are present, whose sources are analyzed