APPARENTLY UNIVERSAL CHANGES IN THE ELASTIC PROPERTIES OF MONOMOLECULAR FILMS

Surface Light scattering has been used to investigate various spread m onolayers at the air-water interface. In particular, the variation of the dilatational elastic modulus has been studied as the films undergo a phase transition from the vapor to a condensed phase. In all cases studied this modulus increases discontinuously on condensation of the film. The increases are, within the uncertainties, apparently universa l, being of magnitude 4 pi when expressed in units of k(B)T/A, where A is the molecular area in the monolayer. This value accords with the p redictions of certain theories of two-dimensional melting.