A generalized regular solution model of a liquid supported monolayer of long chain amphiphile molecules

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Abstract
We describe a generalized regular solution model of a liquid supported monolayer of long chain amphiphile molecules. The model includes the effects of chain flexibility in the surface layer and in the space outside the surface layer, but the neglect of chain–chain interactions outside the surface layer restricts the domain of applicability of the analysis to small to modest surface coverage (up to the critical density). The analysis leads to self-consistent equations for the distribution of molecular configurations and the surface density and pressure. An examination of available data for pentadecanoic acid on water (pH=2) leads to the strong inference that even at infinite dilution individual molecules take up configurations with a large part of the chain outside the surface layer. This inference, and others drawn from the theory, are supported by Monte Carlo simulations reported in the accompanying paper. An extension of the model includes the influence of aggregation of amphiphile molecules on the properties of the monolayer.