A direct measurement of the influence of vapour, of liquid and of oriented monolayers on the interfacial energy of mica
A cleavage technique has been used to measure solid/fluid interfacial energies, and to study directly the effect of various media on these energies. Solid/vapour and solid/liquid interfacial energies were measured by cleaving mica specimens first in an atmosphere of vapour and then in the corresponding liquid. In this way we have a direct means of checking the validity of Young’s equation. Results obtained with water, as representative of a polar medium, and hexane, as representative of a non-polar medium show that Young’s equation holds for systems with zero contact angle. The effect of the humidity of the surrounding atmosphere on the cleavage of mica was also investigated. Water vapour was found to produce a marked reduction in the cleavage energy. In another set of experiments the cleavage technique was used to determine the work done in separating mica surfaces covered with an adsorbed monomolecular layer of fatty acid. The results yield a value of 37 erg/cm 2 for the surface energy of a lauric acid monolayer on mica.