Investigation of dynamic glass transitions and structural transformations in cryovacuum condensates of ethanol

Abstract

An IR spectrometric investigation of the dynamic glass transition of ethanol from the rotationally disordered crystal to the orientationally disordered crystal is carried out. The samples considered are thin films formed from the gas phase at a substrate temperature of T=16K. The measurements are performed using the experimental apparatus which has been described in detail in our recent work. The sample thickness was d=2μm, and the typical rate of annealing is approximately 10K∕min. The results are compared with the phase diagram of solid ethanol proposed by M.A. Ramos et al. We observe good agreement between the temperature intervals of existence of the amorphous and crystalline states. The low-temperature amorphous phase (12–70K) is described by the present authors as amorphous solid ethanol by analogy with the amorphous solid water.

Physical modeling of the formation of clathrate hydrates of methane

“…Temperature range 130-145 K. Observed sharp changes of the measured parameters are related, in our opinion, to the restructuring of the solid phase from the water in ASW through the intermediate state SCL to cubic ice [4,14]. Due to the presence of an intermediate state SCL adsorbed methane receives necessary diffusion mobility to move to the phase boundary and subsequent desorption.…”

“…Thus, a spontaneous increase in pressure in the camera may be connected with the thermodesorption processes occurring in the sample, which are reflected in the characters of the thermograms obtained. This method of thermal desorption was widely used earlier by us and some other authors [4][5][6]. Physical modeling of methane hydrate formation implies the measurement of oscillatory ranges of the condensed films and the subsequent analysis of their transformations under warm-up.…”

On the problem of the existence of a supercooled liquid phase of cryovacuum ethanol condensates

“…Our previous IR spectrometry and thermodesorp tion studies of thin films of cryovacuum ethanol con densates [13][14][15] and comparison of these results with the data obtained in [12,16] allowed us to make some assumptions relative to the existence ranges of the known low temperature forms of ethanol. Figure 1 shows the comparison of the heating curve of a thin film of the cryogenic ethanol condensate [13] with the phase diagram of the monolithic ethanol sample obtained from the liquid phase by ultrafast cooling [12].…”

“…Figure 1 shows the comparison of the heating curve of a thin film of the cryogenic ethanol condensate [13] with the phase diagram of the monolithic ethanol sample obtained from the liquid phase by ultrafast cooling [12].…”

“…Thus obtained thin films of solid ethanol are conventionally determined as cryovacuum condensates. Our IR spectrometry studies and the analysis of thermally stimulated relaxation processes in amorphous ethanol films [13][14][15] indicate the following. At temperatures above T = 70-80 K, the behavior of amorphous cryo vacuum ethanol condensates is similar to that observed in the studies where the samples of solid eth anol obtained from the liquid phase by ultrafast super cooling (quenching) were studied [9][10][11][12].…”