Hemi-micelles structure

The adsorption of many surfactants at the solid/liquid interface may show several steps that are accompanied by various structures on the surface (bilayers, hemi-micelles and micelles). This is represented in detail in Chapter 4. 

In the other cases (for instance, an hydrophobic polymer with grafted hydrophilic groups this time in water), the polymer molecules tend to attach themselves with some physical cross-linking between hydrophobic parts. The increased hydrophobic character of such nodes is susceptible to attract surfactant molecules that form a surrounding hemi-micelle and further contribute to diminish contact with water (see Fig. 13). The whole surfactant plus polymer is building a new structure with its own properties. 

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... 

We analyzed all these structural parameters for the first stable hemi-micelle in each of the systems presented above to determine the effects of the tail length, ionic strength and counterion size on such a structure. In all cases the center of mass of the surface object is located in the water phase, above the Gibbs plane, which is at... 

Figure 5.6 Structural properties of the first stable CigXs hemi-micelles adsorbed at the vapor-water interface. Structural ratio from moment analysis ( ), and from geometry (O) deviation of the centre ofmass from the Gibbs plane ( ). (a) Effect of the ionic strength for Pi, Ny, (b) effect of counterion size for (pj = 0.01.

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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