Surface Tension in Liquids

Abstract

THERE is ample experimental evidence that the free surface of liquids is in a state of tensile stress, but this stress has never been satisfactorily explained in terms of the positions and motions of molecules. It is generally recognized that liquids cannot permanently withstand shear, and yet a two-dimensional tensile stress implies shear in all planes inclined to the plane of the tension. How is this possible? The most acceptable previous explanation is that due to Bakker1, which has recently been discussed by R. C. Brown2; but the Bakker theory is not very satisfying, as it is an attempt to show that the surface of a liquid could be in a state of effective tensile stress without an associated shear stress. The failure to explain the tension stress in the surface of liquids has led many writers to regard it as unreal. Authors who have referred to the stress as a ‘fiction’ include Laplace, Rayleigh and N. K. Adam. Adam3 also writes, “The surface tension does not exist as a physical reality”. J. Rice4, in his commentary on Gibbs' papers on surface phenomena, is at pains to absolve Gibbs from having the notion that the surfaces of liquids are in a state of tension stress.