Charged hemi-micelles

Modeling the Structure and Stability of Charged Hemi-Micelles at the Air-Water Interface... 

In the following, we present results from the thermodynamic and structural analysis of these adsorbed lenses. By taking into account findings from charged surfactant self-assembly in solution, it is expected that various parameters influence the stability and structure of adsorbed charged hemi-micelles at the air-water interface. For instance, it is known that surfactant characteristics, such as the tail... 

The surfactant sodium dodecyl sulphonate (Ci2H2sS03Na) and its sulphate adsorb electrostatically on hematite at low solute concentrations (Han et al., 1973). Hydro-phobic effects operate at high concentrations due to the incompatibility of the hydrocarbon part of the molecule with water. This involves condensation of the alkyl chains at the surface (hemi-micelle interactions), which lowers the free energy of the system and reverses the surface charge. 

At higher ionic surfactant concentrations. Van der Waals interaction between hydrocarbon chains and hydrophobic bonding results in aggregation, forming clusters called hemi-micelles (12.17-21). The aggregation numbers of hemi-micelles are not well established estimates range from 2 to -250 (15.22.23). Surface charge is reduced more rapidly than at lower solution concentrations and is ultimately reversed as solution concentration and adsorption increase so the adsorption bond includes a chemical or specific contribution. 

Lens-type hemi-micelles are predicted to arise at the air-water interface at relatively low bulk concentrations (with respect to the CMC) of charged surfactants with sufficiently long tail. The heads are exposed to the water phase while the tails form the core that enters the vapor phase. The stability of these hemi-micelles increases with tail length and ionic strength, but decreases with the counterion size. However, the excess number of surfactants in the adsorbed hemi-micelles, and also their structures, depend more strongly on the surfactant head properties than on the surfactant tail size, as is the case for spherical micelles. The effect of the tail length on the... 

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