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

Abstract

Abstract 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 (Vm) on deposition similar to EB glass. Interestingly, the samples of the three compounds, which were formed initially as glasses with Vm 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 Vm smaller than that of SCL is briefly discussed by referring to the observations of toluene samples which showed a slightly different Td dependence of Vm and did not show the curious light scattering in the SCL state.