The Electrocapillary Curves of the Phosphatidylcholine Monolayer at the Polarized Oil–Water Interface. II. Double Layer Structure of Dilauroylphosphatidylcholine Monolayer at the Nitrobenzene–Water Interface

Abstract

Abstract Electrocapillary curves have been measured at the polarized nitrobenzene–water interface in the presence of dilauroylphosphatidylcholine (DLPC) in the nitrobenzene phase. DLPC formed a saturated monolayer when the concentration of DLPC was above 10 μmol dm−3. The area occupied by a DLPC molecule in the saturated monolayer was 0.93 nm2, indicating that the monolayer was in the liquid-expanded state. The stability of the monolayer was strongly affected by the electrical potential difference across the interface. The monolayer was stable when the interface was negatively polarized, i.e., the potential in the aqueous phase was negative with respect to that in the oil phase. The potential of zero charge shifted to a negative potential as the adsorption of DLPC increased, which indicated the specific adsorption of lithium ions in the aqueous phase to the head group of the DLPC molecules exposed to the aqueous phase. When the interface was positively polarized, the adsorption of DLPC abruptly decreased and the monolayer appeared to be disrupted.