Statistical Theory of Duplex Films

Abstract

The dissociation treatment of condensing systems is applied to duplex films. Complete agreement with the data on the saturated state of the films of myristic acid published by Adam and by Harkins is obtained on the following assumptions: (i) the momentum of each entire molecule contributes to the monolayer gas pressure; (ii) the interaction potential between the ``liquid ends'' of the molecules is equivalent to an ``intrinsic pressure'' which has the effect of increasing the surface tension at the interface between parent liquid and monolayer; (iii) this intrinsic pressure is derivable from a Lennard-Jones type of interaction potential depending on mean molecular area: W=W0+α/A4.5—β/A3; (iv) the tails of the molecules can form clusters, thus forming micelles in the duplex film, in which there are six bonds per molecule, each with interaction energy ε=—8.8×10—14 erg per molecule. The field constants α, β seem to depend slightly on the nature of the parent liquid, but the energy ε is independent of this. The duplex film therefore appears to have its liquid layer in contact with the parent liquid, the free tails forming the gas layer. More data on different parent liquids are needed before a definite decision on this point can be made.