Liquid–Liquid Relaxation in the Supercooled Liquid State of Ethylbenzene: Thermal Studies Using a Prototype DTA Sensor for the Study of Vapor-deposited Samples

Abstract

A prototype sensor for differential thermal analysis (DTA) was developed for in situ studies of the thermal behavior of molecular films vapor-deposited onto a cold substrate in a vacuum. The system was applied to the study of ethylbenzene (EB). By raising the temperature at a constant rate, we observed in the supercooled liquid (SCL) state a small exothermic peak simultaneously with the characteristic light scattering reported previously. These observations and additional optical experiments on the irreversibility of the phenomena indicated that a structural relaxation occurred from a less stable SCL to a more stable SCL.The behavior of vapor-deposited molecular glasses has attracted growing attention in recent years. 16 We observed indications of liquidliquid structural transformation in the SCL states of EB and related compounds for samples obtained through the glass transition of vapor-deposited glasses.3 These indications were determined through study of light scattering in the samples. The results of the light-scattering study, however, did not provide conclusive proof of the structural change in the bulk of the samples. 7 We thus planned to make in situ thermal measurement on vapor-deposited samples while simultaneously monitoring the scattering of laser light.Sample films were vapor-deposited on cold metal substrates with a thickness of approximately ten micrometers. In our earlier studies on EB, we found a curious intensity depression of the laser light reflected from the sample in the SCL state when we raised the temperature continuously.8 This result was due to temporal light scattering. We recently found that EB and related compounds form glasses with different densities depending on the temperature of the vapor deposition (T d ). 2,3 Glasses, deposited at a T d much lower than the glass-transition temperature (T g ) of the compound, had densities less than those estimated for the SCL at the corresponding temperature, whereas glasses deposited at a T d only slightly lower than the T g had densities larger than the SCL. We abbreviate hereafter the lowdensity glasses as LDG and the high-density glasses as HDG.Interestingly, the samples originally made as LDG exhibited the above-described reflected light depression when the temperature was raised to the region of the SCL state. However, the samples obtained from HDG did not show such a behavior. Figure 1 compares the typical intensity evolutions of the laser light reflected from EB samples originally prepared as LDG and HDG, respectively.3 The rate of temperature elevation was 0.28 K min ¹1. The patterns of the light intensity evolution were analyzed using our previously reported method, 9 and we determined the temperature region where each sample existed as a SCL as indicated in the figure. Note that the sample originally made as LDG exhibited a strong intensity depression (see the arrow) in the SCL state, while the sample originally made as HDG showed no such depression. We have recently come to consider that the depression is caused by light scatteri...

Dynamics of glass-forming liquids. XVI. Observation of ultrastable glass transformation via dielectric spectroscopy

“…The present experiments would have detected an intermediate state with a mobility three times that of the conventional liquid, a case that had been discussed previously. 24 We also anticipate that if IMC behaved analogous to what has been reported for iso-propylbenzene or ethylbenzene, 45,46 our experiments would have provided an indication for a metastable liquid that differs from the conventional supercooled liquid.…”

“…These optical features were observed immediately following the annealing from the ultrastable glassy state, disappeared after annealing, and remained absent for supercooled liquids formed by cooling the melt. 45,46 Capponi et al reported an analogous feature observed by dielectric spectroscopy. 47 On the other hand, a recent SIMS study 26 suggested that the self-diffusion coefficient D of the liquid transformed from ultrastable IMC glass does not differ from the value of D of the conventional supercooled counterpart.…”

One-, Two-, and Three-Dimensional Hopping Dynamics

“…High density glass is obtained by vapor deposition of ethylbenzene on cold substrates, in addition to thermodynamically unstable low density glass [42]. When the temperature is raised in this system, a structural relaxation occurs to the unstable low density glass, while high density glass transforms directly to supercooled liquid [43]. States of WCA spheres also melted when kept at temperature T = 140 for state E, at T = 135 for states A and B, at T = 134 for state C and D, and at T = 131 for state F. State B kept at T = 135 remained to be so for a certain time, i.e., for t = 1087 (i.e., In Figure 12, we show the self van Hove correlation function F (r xyz , t) in the hopping states A, B, C, D, and E of WCA spheres.…”

Nonequilibrium and Relaxation in Deeply Supercooled Liquid of Isopropylbenzene Obtained through Glass Transition from Vapor-Deposited Glass

“…Immediately after this change, the relaxation from LDL to another SCL took place as indicated by the significant depression of the reflected light intensity. 11,22 Note that this depression is not due to the change in the interference condition but is due to light scattering mainly in the bulk of the sample. 11 In addition, it should be emphasized that no indication of crystallization could be detected in this temperature region from Raman spectra and X-ray diffraction patterns.…”

“…11,22 Note that this depression is not due to the change in the interference condition but is due to light scattering mainly in the bulk of the sample. 11 In addition, it should be emphasized that no indication of crystallization could be detected in this temperature region from Raman spectra and X-ray diffraction patterns. 24 When relaxation to the new SCL was almost completed, the transparency of the sample was recovered to half the level of the maximum intensity.…”