Surfactant networks

In skin care products fatty acids are usually partially neutralized with alkaline or amine bases to create a mixture of soap and fatty acid which build a surfactant network to thicken the aqueous phase and also emulsify the oil droplets. The long chain fatty acids deployed for this purpose are normally a mixture of palmitic and stearic acid. A simple formulation for a vanishing skin cream contains about 20% of fatty acid and its potassium soap mixture and 80% water. Cetyl alcohol, glycol monostearate, and glycerol monostearate are common cosurfactants incorporated inside the network. 

The millisecond range-relaxation process is primarily driven by the aggregation of the inverse micelles of the oil additives (Figure 10-1). Networks of micelles exist in equilibrium with free oil additives, ions, and dipoles through diffusion-controU ejection and recapture of surfactant molecules. The recapture is independent of surfactant type, but the exit rates increase with the shortening of the hydrocarbon tail. The interface between polar and nonpolar components of the surfactant network can become polarized, resulting in the... 

What are the essential features of surfactant systems An important ingredient is obviously the repulsion between water and nonpolar molecules or molecule parts, the hydrophobic force. This interaction is however highly nontrivial, and its analysis is still an active field of research [4,22,23]. Qualitatively, it is usually attributed to the strong orientational and positional correlations between nonpolar molecules in solution and the surrounding water molecules. The origin of the interaction is therefore entropic free water forms a network of hydrogen bonds. In the neighborhood... 

PHEMA solubility decreases with increasing ion concentration. As a result, Mikos et al. used salt solutions of varying ionic strength to dilute the reaction mixtures (Liu et al., 2000). It was noted that increasing the ion content of the aqueous solution to 0.7M, interconnected macropores were obtained at 60 vol% water. Surfactants may also be used to control the network pore structure. However, not much work has been done in this area, since surfactants typically work to reduce the surface repulsions between the two phases and form a uniform emulsion. These smaller emulsion droplets when gelled will create a network with an even smaller porous structure. Yet, this is still a promising area of exploration, since it may be possible to form alternate phase structures such as bicontinuous phases, which would be ideal for cellular invasion. 

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