Enthalpic path and enthalpy-relaxation rates of ethylbenzene glasses prepared by vapor deposition at various temperatures, T(D), were examined on heating intermittently with a high-precision adiabatic calorimeter. It was confirmed that when T(D) is in the range 0.79-0.96T(g), the enthalpies elucidated at their preparation temperatures, i.e., T(D), are lower than those of the liquid-cooled glass. The fictive temperature T(f) at which the enthalpy path of each glass crosses the enthalpy curve expected for the equilibrium supercooled liquid was observed to be lowest when T(D) = 0.92T(g) = 105 K. The glasses revealed two remarkable characteristics: first, the temperature of the peak in the endothermic effect, which corresponds to the temperature T(g,dev) of the steepest devitrification, was observed to increase in correlation with the low-enthalpic nature of the glasses. Second, the devitrification manner was quite different between the glasses with T(D) < 0.92T(g) and T(D) ≥ 0.92T(g), even if the two glasses have the same T(f); the former devitrified gradually and the latter relatively sharply.

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Ethylbenzene (EB) films prepared on cold metal substrates by vapor deposition in vacuum show a curious light scattering in the supercooled liquid (SCL) state when the temperature is raised at a constant rate. To investigate the cause of this phenomenon, we examined the behavior of similarly prepared samples of a series of alkylbenzenes. We found that the vapor-deposited glass of propylbenzene (PB) and isopropylbenzene (IPB) showed a deposition-temperature (T d ) dependence of the initial molar volume (V m ) on deposition similar to EB glass. Interestingly, the samples of the three compounds, which were formed initially as glasses with V m much larger than that of SCL at the same temperature, exhibited the curious light scattering when they transformed to SCL states after the temperature elevation to above their glass-transition temperature, while the corresponding samples with initial V m smaller than that of SCL did not exhibit this light scattering. On the basis of these observations, a hypothesis on the cause of the light scattering in the SCL state is proposed in relation to structural transformation between different SCL states. A microscopic mechanism of the formation of a high-density glass with V m smaller than that of SCL is briefly discussed by referring to the observations of toluene samples which showed a slightly different T d dependence of V m and did not show the curious light scattering in the SCL state.We have studied the structure and relaxation behavior of amorphous molecular systems prepared by vapor deposition on cold metal substrates. 16 The samples were films with a thickness of about 10¯m. Such amorphous samples usually tend to crystallize when they are annealed with temperature elevation. 16 However, vapor-deposited amorphous samples of certain compounds undergo a glass transition and transform into supercooled liquid (SCL) states by temperature elevation without experiencing crystalline states. 710 Similar phenomena have been known for a variety of bulk amorphous materials prepared by liquid quenching.1113 Such special amorphous states are called glasses by analogy with conventional glass. A common structural feature of these glass-forming molecular compounds is their flexibility which permits various intra-and intermolecular conformations and hinders crystallization.We found that glass samples of ethylbenzene (EB) and related alkylbenzenes could be prepared by vapor-deposition with good reproducibility. We studied the properties of these materials using laser light interference in film samples.14,15 One of the remarkable observations during these studies was that the density and relaxation behavior of the glass state systematically depended upon the vapor-deposition temperature (T d ). 15 Glass samples deposited at a T d much lower than the glass-transition temperature (T g ) had a lower density than that estimated for the SCL state at the same temperature. In this paper, we call such a glass "low-density glass" (LDG). In contrast, glass samples deposited at a T d close to T g sometim...

A novel method for estimating the refractive index and density of vacuum-deposited molecular glasses was invented. It is based on the analysis of the interference of the light transmitted through film samples. Molar volumes of toluene, ethylbenzene, and propylbenzene in the glass states were thus elucidated. The volume just after the sample deposition at 78 K was larger by 4−10%, depending on the size of the substituent on the phenyl ring of each compound, than the fictitious value for the supercooled liquid estimated at the same temperature. By temperature elevation at a constant rate, the volume increases first by the thermal expansion of the glass and next decreases rapidly in a narrow temperature region just below the glass-transition temperature. This decrease is attributed to the structural relaxation in the glass, and its magnitude is related to the size of the substituent. Excess volumes included at the initial sample deposition are discussed in relation to the excess enthalpies reported for similarly prepared molecular glasses.

The short-range structure of the neat fluid of fluoroform (CHF3) is investigated around the gas−liquid critical point by measurements of spontaneous Raman spectra of the C−F symmetric stretching (ν2) and the C−F3 symmetric deforming (ν3) modes. The spectra are obtained at reduced temperatures 0.96 ≤ T r = T/ T c ≤ 1.06, the conditions of which permit isothermal studies in the gas, liquid, and supercritical states as functions of pressure and/or density. As the density increases, the spectral peaks shift toward the lower energy side and spectral widths become broader. In the supercritical region, the amount of shifting shows nonlinear density dependence, while the width becomes anomalously large. We analyze these density dependences along vibrational coordinates by the perturbed hard-sphere model. The amount of shifting is decomposed into attractive and repulsive components, and the changes of attractive and repulsive energies are evaluated as functions of density and packing fraction, both of which are continuously varied by a factor of 50. For both vibrational modes, the spectral shift consists principally of the attractive component at all densities and temperatures. Here we evaluate local density enhancement as a function of bulk density by the use of the values of attractive shift and by the use of dielectric analysis. Local density enhancement is highest at the bulk density, where the spectral width becomes anomolously broad. We analyze the density dependences of widths by comparing the experimental values with calculated homogeneous and inhomogeneous widths. The experimental results agree with the theoretical calculations. It is elucidated that the main contribution to width is density inhomogeneity. By comparing short-range structure studied in the present study with long-range structure previously studied by small-angle X-ray scattering, we found that the vibrational motion becomes significantly affected by the dielectric structure as the correlation length of the density fluctuation grows longer than the size of a first solvent shell of CHF3. Under that situation, the ν2 mode is more sensitive than the ν3 mode to the dielectric structure in the vicinity of a vibrating molecule.