Monte Carlo simulations of a three-dimensional lattice model of an amphiphile−solvent system are
presented and examined for their usefulness in predicting the thermodynamics of self-association of
amphiphiles in solution. The size distribution of the aggregates obtained from the simulations is usedin
combination with the mass action modelto obtain the thermodynamic properties of the solution of aggregates
and to obtain expressions for the coefficients of an empirical equation for the Gibbs energy available in
the literature for aqueous nonionic surfactant solutions. The results are in good agreement with the
empirical model, and the essential microstructural features and thermodynamic properties of the micellar
solution can be extracted reasonably well using such an empirical fitting of the simulation data. The effects
of the lengths of the solvophobic and solvophilic sections of the amphiphile on critical micelle concentration
extracted from the simulations are consistent with experimental results reported for several nonionic
surfactants in water.
We use a lattice-based Monte Carlo method presented recently for micellar solubilization (Talsania et al. J. Colloid Interface Sci. 1997, 190, 92) to determine the phase behavior in surfactant-solute-solvent systems and to examine the locus and extent of solubilization of solutes in micelles as a function of the solute hydrophobicity and chain length. A novel method, based on the distribution of solute in clusters of different sizes, is developed to study the phase behavior of the solute in the absence and presence of surfactant. The results obtained from these simulations are compared with estimates based on quasichemical theory to determine the applicability of this theory to micellar systems. Addition of surfactant to a solutesolvent system first leads to a decrease in the solubility of the solutes prior to a subsequent increase at higher surfactant concentrations. An examination of micellar shapes shows that the surfactant studied forms roughly spherical micelles. However, the presence of solute induces coexistence of spherical and oblong micelles.
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