Behavior of Glass and Supercooled Liquid Alkylbenzenes Vapor-Deposited on Cold Substrates: Toward the Understanding of the Curious Light Scattering Observed in Some Supercooled Liquid States

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 (Td) 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 Vm 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 smaller than that of SCL is briefly discussed by referring to the observations of toluene samples which showed a slightly different Td dependence of V-m and did not show the curious light scattering in the SCL state.