Estimation of the polar parameters of the surface tension of liquids by contact angle measurements on gels

In a previous paper it was shown that negative interfacial tensions between predominantly monopolar surfaces (i.e., surfaces with mainly H-acceptor properties) and polar liquids are real phenomena. Such negative interfacial tensions do however decay rapidly. For miscible liquids, the decay of the interface is, in general, so rapid that it practically excludes measurement of interfacial tension. However, if one liquid is present in the form of a gel, and if the other liquid is placed as a drop upon the gel, there is often enough time to measure contact angles. This may be done at various concentrations of the liquid encased in the gel, and an extrapolation made to zero concentration of the gelling agent. With this method we found the existence of negative interfacial tensions at liquid/liquid interfaces.