The surface potential of Langmuir monolayers revisited

The surface potential characterization of Langmuir monolayers of simple, aliphatic compounds is revisited. Analogously to what has already been observed for fatty acids, the monolayer surface potential for esters and alcohols is close to zero at very large areas per molecule and only starts to increase at a given critical area. No problems of reproducibility are noted, which means that domains known to exist even in earlier stages of monolayer compression do not make the monolayer macroscopically heterogeneous. The appearance of a critical area is consistent with findings from a number of other experimental techniques employed by research groups around the world, including lateral conductance, optical reflectance, Maxwell displacement current, and ellipsometry.