Simultaneous study of mechanical and electrical properties of a self assembled insoluble monolayer by axisymmetric drop shape analysis (ADSA)

A novel technique has been devised to measure mechanical and electrical pro perties of a lipid monolayer in contact with an electrolytic solution and s upported by a metal electrode. The technique is based on a sessile drop app aratus in which the surface of a mercury drop, covered with the lipid film, can be alternately increased or decreased, while optically measuring the d rop shape, hence the interfacial tension, by the ADSA technique. At the sam e time the film polarization state is controlled by a voltage clamp circuit and differential capacitance is measured by a lock-in amplifier. By this t echnique it is possible to obtain, e.g. the relation between surface pressu re and differential capacitance, or surface pressure and polarization, that cannot be obtained with any other technique in a single experiment and on a single film. Films formed on the drop surface have been shown to be stabl e for many hours.