Mechanism of the clouding phenomenon in surfactant solutions

The possible mechanism for clouding in surfactant solutions of nonionic and mixed ionic-nonionic surfactants is reviewed. Semiquantitative arguments to predict the trends in changes of clouding temperatures in mixed systems are proposed. Results for Triton X-100 and additives, sodium dodecyl sulfate and salicylic acid, are presented. A methodology for systematic interpretation of light and small-angle neutron scattering (SANS) results in uncharged colloidal systems is proposed by taking advantage of the smallness of the ratio of the range of attractive interaction to the diameter. The use of these methods is illustrated by estimating the van der Waals depth of the intermicellar potential in nonionic micellar systems. The experimental results seem to indicate that the well depth increases quadratically with temperature. The relation of this temperature dependence to hydration experiments is discussed. This procedure is generalized to include Coulomb interactions as a perturbation and is demonstrated by application to experiments on mixed nonionic and ionic surfactants. These results appear to show the phenomenon of charge condensation