Acetonitrile aqueous solution has an upper critical solution temperature (UCST) at 272 K at c ) 0.38 (c represents the mole fraction of acetonitrile). To study quantitatively how the mixing scheme of the solution changes as a function of concentration and temperature, the concentration fluctuation, the Kirkwood-Buff parameters, and individual density fluctuations for acetonitrile and water were obtained by means of smallangle X-ray scattering experiments at 273, 279, and 298 K in the range of 0.0 e c e 0.5. The values of concentration fluctuation became larger close to UCST and exhibit a maximum at c ) 0.38. The mixing scheme of acetonitrile aqueous solution is discussed from the point of view of inhomogeneity of molecular distribution.

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Flow (rheological) properties and dynamic viscoelasticity of concentrated solutions of a hybrid surfactant containing a fluorocarbon chain and hydrocarbon chain within a single molecule were analyzed. The results indicated that the viscosity of the hybrid surfactant solution is not proportional to the increase in its concentration, and it showed an anomalously large value around a 10 wt % solution. It was also indicated that the surfactant solution in this range of concentration behaves like a viscoelastic substance with a characteristic of rubber like elasticity.

Self-diffusion coefficients and viscosities for the saturated hydrocarbons having six carbon atoms such as hexane, 2-methylpentane (2MP), 3-methylpentane (3MP), 2,2-dimethylbutane (22DMB), 2,3-dimethylbutane (23DMB), methylcyclopentane (McP) and cyclohexane (cH) were measured at various constant temperatures; obtained results were discussed in connection with their molar volumes, molecular structures and thermodynamic properties. The values of self-diffusion coefficients as the microscopic property were inversely proportional to those of viscosities as the macroscopic property. The order of their viscosities was almost same to those of their melting temperatures and enthalpies of fusion, which reflect the attractive interactions among their molecules. On the other hand, the order of the self-diffusion coefficients inversely related to the order of the melting temperatures and the enthalpies of the fusion. Namely, the compound having the larger attractive interaction mostly shows the less mobility in its liquid state, e.g., cyclohexane (cH), having the largest attractive interaction and the smallest molar volume exhibits an extremely large viscosity and small self-diffusion coefficient comparing with other hydrocarbons. However, a significant exception was 22DMB, being most close to a sphere: In spite of the smallest attractive interaction and the largest molar volume of 22DMB in the all samples, it has the thirdly larger viscosity and the thirdly smaller self-diffusion coefficient. Consequently, the dynamical properties such as self-diffusion and viscosity for the saturated hydrocarbons are determined not only by their attractive interactions but also by their molecular structures.