Resistance oscillation of a Millipore DOPH model membrane accompanying structural changes.

A Millipore DOPH model membrane is composed of a Millipore filter whose pores are filled with dioleylphosphate (DOPH), and its electric resistance increases by a factor of 10(4) when Ca2+ ions are combined with it. The concentration of CaCl2 which increases the membrane resistance depends on the density of DOPH adsorbed in the filter and the initial KCl concentration. The surface structure of the membrane changes at the same time as the membrane resistance increases. The structural changes can be directly observed by a stereoscopic microscope: a considerable decrease of the hydrophilic regions of the membrane is caused by the Ca2+ ions. The membrane resistance which become higher with Ca2+ ions oscillates while a constant current and a static pressure stimuli are applied to the membrane. The frequency is dependent of these stimuli. These stimuli change the local membrane surface structure to make the hydrophilic areas. It is conceivable that the structural changes are caused by replacing Ca2+ ions with K+ ions in the hydrophilic bases of DOPH molecules.