The heat capacities of glassy and liquid toluene and ethylbenzene were measured with an adiabatic calorimeter. Both samples were doped with about 10% of benzene to suppress crystallization. The effects of the doping were corrected for by assuming the additivity of the heat capacities of toluene (or ethylbenzene) and benzene. The configurational entropies of several glass-forming liquids, including toluene and ethylbenzene, were calculated as functions of temperature from their heat-capacity data. For these calculations, the vibrational heat capacities were determined by the least-squares fitting of the Debye and Einstein functions to the experimental values using auxiliary spectroscopic data from the literature. The size of cooperative rearranging region (CRR), which was first conceived by Adam and Gibbs, was calculated from the configurational entropy in a simplifying approximation that neglects distribution of CRR size and internal entropy of CRR. For all of the systems examined, the size of CRR increases with decreasing temperature and is frozen-in at four to eight molecules per region at the glass-transition temperature.

The dynamics of water molecules confined in MCM-41 was investigated by quasi-elastic neutron scattering. The measurement was performed for three water-filled MCM-41 samples with different pore sizes in the temperature range 200-300 K. The spectra were analyzed by using a model employed by Teixeria et al. in a study for bulk water. This model is composed of two motions of water molecules: rotational and translational diffusions. For the translational diffusion, water molecules in MCM-41 are, on the whole, less mobile than those in bulk water, and the mobility is decreased by narrowing of the pore size. The residence time of translational diffusion of the confined water molecules shows the Arrhenius type of temperature dependence, which is in contrast to a non-Arrhenius behavior for bulk water. This implies that a growth of the hydrogenbond network of water is hindered in a confined space by surface field. Spectra of MCM-41 sample having monolayer water were also measured and could be analyzed with a model in which only rotational diffusion is an allowed motion of the monolayer water molecules.

Quasielastic neutron scattering (QENS) spectra of water-filled MCM-41 samples (pore diameters: 21.4 and 28.4 Angstrom) were measured over the temperature range 238-298 K and the momentum transfer range 0.31-0.99 A(-1) to investigate the dynamics of confined water molecules. The spectra, which consist mainly of contributions from the translational diffusion of water molecules, were analyzed by using the Lorentzian and the stretched exponential functions. Comparison of the fits indicated that the latter analysis is more reliable than the former one. The fraction of immobile water molecules located in the vicinity of the pore walls, which give an elastic component, was found to be 0.044-0.061 in both pores. The stretch exponent beta was determined as 0.66-0.80. It was shown that the translational diffusion of water molecules in the pores is decelerated by confinement and that the deceleration becomes marked with a decrease in pore size. The ratios of the translational diffusion coefficient D(T) of confined water to that of bulk water at room temperature were within a range of 0.47-0.63.

The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C[triple bond]N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 A (C14), below which it is not frozen. In addition, phase changes between alpha-type and beta-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Deltagamma(l/alpha) = 22.4 mJ m(-2) for the liquid/pore surface (ps) and alpha-type/ps, and Deltagamma(alpha/beta) = 3.17 mJ m(-2) for alpha-type/ps and beta-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol(-1) compared to the bulk value of 12.7 kJ mol(-1). The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.

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