The conditions for obtaining the electrocapillary curves of the dilauroylphosphatidylcholine (DLPC) monolayer formed at the polarized nitrobenzene–water interface have been studied using the pendant drop method. To facilitate the measurement, the system for the interfacial tension measurement, including the computer software for the data handling, has been developed based on digital image processing of the video image of a pendant drop. The 95% confidence interval of the measured interfacial tension value was ±0.06 mN m−1. The time required to measure an electrocapillary curve with 30 points was 30 min, while the time necessary to convert the image data to the interfacial tension was 1 min. The potential drop across the monolayer has been demonstrated to influence the stability of the monolayer strongly. The DLPC markedly lowered the interfacial tension by forming a stable monolayer when the interface was polarized so that the aqueous phase has a negative potential with respect to the nitrobenzene phase. On the other hand, when the aqueous phase became positively polarized, the adsorbed DLPC molecules started to desorb from the interface, giving rise to the disruption of the monolayer. The electrocapillary curves only in the former potential range were found to be thermodynamically meaningful.
Electrocapillary curves at the polarized interface between a nitrobenzene solution of tetrabutylammonium tetraphenylborate (TBATPB) and an aqueous solution of lithium chloride at various concentrations of TBATPB and LiCl have been measured by the drop time method using a dropping electrolyte solution electrode at 25 °C. The relative surface excesses of tetrabutylammonium and tetraphenylborate ions in the nitrobenzene phase and of lithium and chloride ions in the aqueous phase were well described by the Gouy-Chapman theory of diffuse layers for both sides of the interface. A model of the electrical double layer for the nitrobenzene–water interface is presented, in which an ion-free inner layer consisting of laminated monolayers of water and nitrobenzene is sandwiched by the two diffuse layers on each side of the interface. The potential difference across the inner layer, which was estimated to be ca. 20 mV at the potential of zero charge, was found to be dependent on the surface charge density and to be nearly independent of the electrolyte concentration.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.