The Effective Microviscosity and Polarity of Micelles

The effective microviscosity and polarity of organized molecular assemblies have a great influence upon photoreaction including diffusion and interaction of polar and 

The effect of added alcohols upon the microviscosity of micelles was studied by Turro et al. [76]. The low-molecular alcohols reduce the microviscosity of CTAB micelles. The high-molecular alcohols do not influence the microviscosity. Schinitzky et al. observed a phase transition of a bilayer membrane by the fluorescence depolarization technique [75]. 

The use of the picosecond technique enabled Pouligni et al. to observe the reorientation kinetics of 3,3 -diethyloxadicarbocyanine by absorption anisotropy in microemulsions of Aerosol OT (AOT) and methyl alcohol in cyclohexane [84, 85]. 

A further technique to study the microviscosity of micelles is based on the measurements of intramolecular exciplex formation [86-89]. In solvents possessing viscosities exceeding 2 cPs, the rate of the intramolecular exciplex formation depends upon the viscosity of the solvent and not upon its polarity [86]. In contrast to the intermolecular exciplex [87] whose formation rate is influenced by the distribution of the reactants among the micelles, the formation of the intramolecular exciplex is controlled by the relative rotation of two parts of one molecule only. The values of the microviscosity obtained with this method are in good agreement with ones obtained by the depolarization technique [87]. 

The rate of a photo-isomerization reaction can be used to characterize the structure of micelles [90]. The dark-reaction of the spiropyran cycle cleavage, yielding the corresponding merocyanine, is controlled by the high microviscosity of micelles. 

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