PH- AND IONIC-STRENGTH-DEPENDENT PERMEATION THROUGH POLY(L-LYSINE-ALT-TEREPHTHALIC ACID) MICROCAPSULE MEMBRANES

The permeability to both anionic and cationic ions, the size, and the electropheretic mobility of poly(L-lysine-alt-terephthalic acid) microcapsules have been measured. The permeation rate and the size are both strongly pH dependent, exhibiting a sharp change in the pH region between 4 and 6, with their minima at pH 4. On the other hand, the electrophoretic mobility measurements show that this membrane has the isoelectric point between pH 2.3 and 2.6. These phenomena are considered to be caused by the shrinkage of the microcapsule membrane, as is seen in polyelectrolyte hydrogel membranes. This shrinkage can be made by an ion-complex formation between fixed charged groups, -NH3+ and -COO-, located in the polymer chains.