approach to the matter was to regard the micelles as a sepa-The densities and viscosities of binary aqueous mixtures of polyrate phase (5-8). The resultant treatment can be expected (ethylenoxide)hexanols [C 6 H 13 (OCH 2 CH 2 ) m OH, C 6 E m ] (m ร
3, to fare no worse than the mass-action treatment and is easier 4, and 5) have been studied in the micellar composition range. to apply. The ambiguity of these two models can be resolved For the same surfactants the self-diffusion coefficients in mixtures by applying the thermodynamics of small systems or the with heavy water have been determined by the spin-echo pulsed Kirkwood-Buff theory (9) of solutions of nonionic surfacfield gradient method. The volumetric data are interpreted by tants (10-15). The development of explicit theories describmeans of the phase separation model, and values of the CMC, ing micellar aggregation beyond thermodynamic treatments volume change, and standard free energy change of micellization are obtained. From the viscosity data the hydration numbers of is a difficult problem because the molecular interactions inthe surfactant hydrophilic head in the micellar state are computed; volved are too complex to be described in terms of statistical they are in agreement with those obtained from HDO self-diffusion mechanics so that usually models are used for linking micelle data. The surfactant self-diffusion data are used to calculate the formation to molecular solution structures. The model most apparent micelle radius and the aggregation number. The micellicommonly adopted is the well-known hydration model of zation parameters obtained for the different surfactants are com-Nemethy and Sheraga (16), assuming two different kinds pared and discussed.