The Molecular Mechanism of Capillary Phenomena

Abstract

AN important question for the theory of capillarity is this: Is it necessary, in order to explain the observed phenomena, to conclude that there is, in the surface of a liquid, any differentiation of the molecular arrangements and forces from those prevailing in the interior, of such a nature that there is a skin possessing a tension parallel to the surface? Many writers appear to assume that, because the free energy associated with each unit of area of the surface is most conveniently replaced in calculations by a tension parallel to the surface, there must be some special structure in the surface which produces this tension physically. Although any free energy resident at the surface may mathematically be considered as the product of a “surface tension” and the area, there is no justification in this fact for concluding that the molecular arrangements and forces at the surface resemble those in a stretched membrane. Indeed, probably all attempts made to explain the molecular structure of surfaces, which have assumed such a contractile mechanism, have been complete failures.