Stability in Soap Films

Abstract

SOAP films exhibit a stability (permanence and mechanical strength) which is without parallel in films of water or other pure liquids which contract almost instantaneously to spherical droplets under the influence of surface tension. In a letter to NATURE of May 31, p. 815, Mr. Green attributes this stability to “stratifications … almost certainly pervading the whole film”. This conclusion is directly opposed to the view, now widely held, that soap films have a ‘sandwich’ structure, as I have called it (J. Phys. Chem., 34, 263; 1930); that is, that they consist of a pair of surface layers adsorbed at the liquid/air interface and enclosing a layer of liquid, identical in composition with the channel of liquid around the boundary of the film and its rigid support (often called the Gibbs' ring) and with the solution from which the film was made. In reply to Mr. Green's contentions, there is no evidence that soap films have greater stability than is to be expected from the sandwich structure. There is no reason to suppose that any degree of strength would result from the structure suggested by him, nor that such a structure exists except in abnormal and rare cases. The evidence for these opinions is as follows: