Abstract
The zeta potentials of insulin microcrystals at the various pH were obtained by using the microelectrophoretic method. The zeta potential in the higher pH region than the isoelectric point of pH5.5 steeply decrease with increasing pH, although in the lower pH region the value gradually increase with decreasing pH. The morphological change from dendritic to polyhedral crystals at about pH5.5 found in the previous experiments was explained by the asymmetrical character of the zeta potential around the isoelectric point. The dependence of the zeta potential on the size of the crystals was also established at pH6.5, i.e., the larger crystals have the larger negative potentials, although according to the theory of Smoluchowski the zeta potential is independent on a particle size.
