A fractal model for the molecular organization in the alkylbenzenesulphonate/electrolyte/water system

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Abstract
Under conditions where individual molecules are no longer soluble, the association of amphiphiles occurs as a sequence of growth and aggregation processes: the formation of dimers, bilayers and multilayer assemblies culminates with the production of myelin cylinders and chains or spherulitic arrays of focal-conic units. We have examined this process using the alkylbenzenesulphonate/electrolyte/water system as a model. The phase diagram was obtained using optical microscopy. The kinetics of the aggregation process were followed by lightscattering measurements and the structures of the one- and two-phase regions were examined by optical microscopy and freeze-fracture electron microscopy. The fractal nature of the aggregation process was investigated using an indirect Fourier transform study of the lightscattering data. The fractal character of the whole self-assembly process was confirmed and an experimental value of 2.17 was determined for the fractal dimension (in close agreement with the expected theoretical value of 2.16).