Molecular interaction in monolayers: I—complexes between large molecules

Abstract

In previous communications (Rideal et al . 1933, 1935) from this laboratory it has been shown that the course of chemical reactions proceeding in monomolecular films or monolayers at air liquid interfaces, can be followed by means of observation of the changes in phase boundary potential and surface pressure or tension. It seemed possible that a further advance in the elucidation of the complex mechanism of lytic, sensitizing, agglutinating and immunity reactions might be made by a closer study of the behaviour and interaction of a number of biologically active substances in the form of monolayers, especially as it appears that several of these biological processes take place under conditions similar to those existing in the films. It is found that if an extremely dilute solution of a suitable molecular species be injected under a monolayer of another, under the correct inter­acting conditions, a phenomenon which we may term film penetration is observed. The chief characteristics of film penetration are an immediate large rise in surface pressure of the film, a decrease or increase of the surface potential, according to the magnitude of the dipole moments of the pene­trating polar group, compared to that of the film-forming molecule, and the strong stability of the resultant new film. It appears that the process of penetration is completed when a mixed film, consisting of equimolecular proportions of the original film material and the penetrating substance, is formed. The final value of the phase boundary potential is found to correspond exactly with that shown by the equimolecular mixed film spread on the surface and compressed to maximum pressures.