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.

Extensive studies on polymer thin films to date have revealed their interesting but unusual properties such as film thickness dependence of glass transition temperature Tg and thermal expansivity. Recent studies have shown that the lower Tg is not always related to the higher mobility in polymer thin films, which contradicts our current understanding of the glass transition process. In this work, we report the results of inelastic neutron-scattering measurements on polystyrene thin films using two spectrometers with different energy resolutions as well as ellipsometry measurements. The results are interpreted in terms of cooperatively rearranging region and motional slowing down due to the surface effect that explain plausibly the anomalous relationship between the glass transition temperature Tg and the molecular mobility in thin films.

Dynamics of water contained in the pores of alumina gel as studied using a combination of the high and medium resolution quasi-elastic neutron scattering (QENS) technique at room temperature and extending to the supercooled region is reported. In the single particle picture of the dynamics of water molecules in confined geometry (Volino-Dianoux model), two types of water are found to be present in the pores of alumina gel. Some water molecules are attached to the surfaces (localized) and others undergo diffusion within the otherwise available space in the pores. The localization radius and diffusion constant (Dloc) characterizing the local dynamics and also the diffusion constant (Dt) and residence time (τ0) of the water molecules diffusing inside the alumina gel pores are obtained at different temperatures. Water molecules are found to undergo restricted diffusion in the pores at higher temperatures, which approach the bulk-like behaviour in the supercooled region.

The local dynamics of 10 substituted polyacetylenes in the glassy state have been investigated using a quasielastic neutron scattering technique in a time range of picoseconds to several tens of picoseconds to see a relationship between the local mobility and the gas permeability of these polymers. Even in the glassy state, these polymers show quasielastic scattering components, suggesting that certain stochastic motions occur in the glassy state. The dynamic scattering laws S(Q,ω) of the quasielastic components were well fitted to the sum of two Lorentzians, i.e., the narrow (slow) and broad (fast) components. It was found that both the relaxation rate Γ n and the fraction An of the narrow (slow) component show positive correlations with oxygen permeability coefficient (PO 2 ), suggesting that the local mobility of the matrix polymers plays an important role in gas permeability. We then defined local flux F, which is the product of Γn and An, as a measure of the local mobility to find that F is proportional to the diffusion coefficient of O2 gas (DO 2 ), i.e., F ∝ DO 2 . To explain and discuss this relation, we have proposed a random gate model, where mobile side groups in the matrix polymer act as a gate for gas diffusion.

No abstract

No abstract

No abstract

We report inelastic neutron scattering measurements on polystyrene thin films in a glassy state in the meV region. We found in elastic scattering that the mean square displacement decreased with film thickness, and hence the corresponding force constant f increased. In inelastic and quasielastic scattering, we observed the so-called boson peak at around 1.5 meV and the picosecond fast process for the first time in thin films, both of which decreased in intensity with film thickness. These results were discussed in terms of the potential hardening due to the confinement of polymer chains and/or the interfacial dead layer.