Maxwell Displacement Current across Langmuir Phospholipid Monolayers Mixed with Azobenzene by Photoisomerization

Mixed monolayers composed of phospholipid and fatty acid containing azobenzene on a water surface were investigated by the Maxwell displacement current (MDC) measurement method. The transient displacement current pulses were generated across mixed monolayers due to the photoisomerization of fatty acid containing azobenzene by alternating irradiation of ultraviolet and visible light because the condensation of pure azobenzene monolayers was loosened by the introduction of phospholipids into the monolayers. The charge flow and Maxwell displacement currents generated during light irradiation were also investigated in connection with monolayer compression cycles. It was found that MDC pulses were generated over the entire range of molecular area, and the maximum of MDC appeared at the molecular area just before the initial rise of surface pressure in both first and second compression cycles, although the surface pressure-area isotherm of the mixed monolayers gives a shift with respect to the molecule-area axis with the cyclic application of monolayer compression. Copyright 1997Academic Press