Alkyl chain aggregation, effect

Effect of Alkyl Chain Aggregation in Organoclay—Bilayer versus Monolayer Arrangement... 

What characterizes surfactants is their ability to adsorb onto surfaces and to modify the surface properties. At the gas/liquid interface this leads to a reduction in surface tension. Fig. 4.1 shows the dependence of surface tension on the concentration for different surfactant types [39]. It is obvious from this figure that the nonionic surfactants have a lower surface tension for the same alkyl chain length and concentration than the ionic surfactants. The second effect which can be seen from Fig. 4.1 is the discontinuity of the surface tension-concentration curves with a constant value for the surface tension above this point. The breakpoint of the curves can be correlated to the critical micelle concentration (cmc) above which the formation of micellar aggregates can be observed in the bulk phase. These micelles are characteristic for the ability of surfactants to solubilize hydrophobic substances in aqueous solution. So the concentration of surfactant in the washing liquor has at least to be right above the cmc. 

The formation of amphiphilic aggregates can be seen as a compromise between the tendency of alkyl chains to avoid contact with water and the strong affinity of the polar groups to water. A thermodynamic description of micellar systems should thus include both these aspects. The electrostatic effects are discussed in Sect. 6 so we will concentrate here on the interactions involving the nonpolar part of the amphi-phile. 

---