Dynamic Aspect of a Phase Transition in DOPH-Millipore Membranes

For an artificial membrane in which dioleyl phosphate (DOPH) is infiltrated into pores of Millipore filter, a relaxation of electric caracitance of the membrane in a solution was investigated after an abrupt change of salt concentration. Relaxation curves of sigmoid types were observed after an increase of salt concentration, while the curves were of exponential types after a decrease. These facts suggest us that hysteresis loops of electric capacitance or this membrane observed for a cyclic variation of salt concentration belong to a different type from the usual ones originating from the first-order phase transition. It is shown that these electric characteristics of the membranes can be explained well on the basis of a model that dioleyl phosphate molecules make transitions among three phases composed of droplets, spherical micells and multi- or bilayer leaflets.