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6559spacing and orientation of the chains. It should be pointed out here that the difference between bulk hydrocarbon and apparent core densities can be explained by two reasons: (a) the two phases are different in the number of terminal hydrogen atoms per alkyl chain, and (b) the molar volume of the terminal hydrogen atom in micelles is significantly less than that in the bulk.Finally, an attempt is made for guessing the number of solvent molecules penetrated in the micellar core. The total volume occupied by solvent molecules is A@(H20) = P ( H ) -9,(H). By definition, the molar volume of solvent molecules inside the micelles is the same as in the bulk; thus, w = A@(H20)/Vw*, resulting in w = 0.45. This result is in good agreement with the upper limit obtained from SANS;2 the agreement of results originating from totally different considerations and experimental methods suggests that the present approach to w may not be entirely arbitrary.Small-angle X-ray scattering measurements have been carried out on tert-butyl alcohol (TBA)-water mixtures at 28, 40, and 55 "C. The temperature effects in the concentration fluctuation and the Kirkwood-Buff parameters have been studied.Debye's correlation length has also been determined for each temperature. With the increase of temperature, the fluctuation becomes larger and the correlation length becomes longer, which indicates that the microscopic demixing of the mixture proceeds as the temperature is raised. The temperature and concentration dependences of the mixing state of the TBA-water solution are discussed.

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Small-angle X-ray scattering measurements have been carried out on ZerZ-butyl alcohol (TBA)-water mixtures at 20 °C.The obtained zero-angle scattering intensities are used together with the isothermal compressibilities and the partial molar volumes to obtain the fluctuations in the particle number and concentration. The values of the concentration fluctuation obtained from X-ray scattering are in agreement with those from light scattering experiments. The concentration dependence of the Kirkwood-Buff parameters has been determined from the concentration fluctuations. The mixing state of the solution has been discussed.