EMULSIONS AND FOAMS 389 compound to such systems often forms a complex with the surface active agent which produces a much more stable emulsion or foam. The evi- dence suggests that the resulting complexes form liquid crystal structures that are much less hydrophilic and more solid than the surface active agents themselves and therefore have more tendency to remain at the pro- pellant-water interface. The oriented liquid crystal nature of molecular complexes with their attendant layers of oriented water molecules suggests that the interfacial region around an emulsified propellant droplet can be viewed as con- sisting of alternating shells of oriented water and molecular complex molecules. The propellant interface would consist of a monolayer of adsorbed molecular complex molecules with the polar heads oriented towards an adjacent hydration layer. The hydration layer of water mole- cules in turn would be surrounded with a bimolecular shell of complex molecules with the polar heads on one side of the shell oriented towards the inner hydration layer and the polar heads on the other side oriented towards an outer hydration shell. This configuration of alternating layers of oriented water and bimolecular complex molecules would ex- tend into the bulk phase with diminishing orientation until it disap- peared. ß '-- SURFACTANT O• FATTY ALCOHOL ii,,,!i,i • ,,:[ • .• ' PHASE INTERFACIAL REGION Figure 1. H•pothetical structure of a molecular complexed interfacial fihn at a propellant- water interface An idealized illustration of this type of structure is shown in Fig. 1. It is patterned after the interfacial structures proposed by Cockbain (33) for soap-stabilized emulsions. It could almost be considered a large spherical micelle except that the propellant is not solubilized and con- stitutes a major portion of the structure. The propellant droplet is the core of the spherical structure with alternating layers of oriented water and surface active agent complex radiating outwards into the bulk phase. (Received September 24, 1969)

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