Excess Volume of Vapor-Deposited Molecular Glass and Its Change Due to Structural Relaxation:  Studies of Light Interference in Film Samples

Abstract

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.

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

“…As has been described in our previous papers, 4,14,15,17 laser light reflected from the sample on a metal substrate showed a periodic change in intensity as sample thickness increased via constant-rate vapor deposition. This was due to changing conditions of the light interference in the sample.…”

“…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.…”

“…15, and the results for TL and PB at T d around 78 K reproduced well the corresponding data reported in our previous paper. 14 We plotted in Figure 3 the initial V m values of all samples as a function of T d . The initial V m of the glasses of the four compounds on deposition was much larger than that estimated for SCL at the same temperature (dashed lines in Figures 2 and 3) if T d was much lower than T g , and the initial V m tended to be smaller as T d was higher.…”

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

“…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.…”

“…This is due to the difference in the interference condition which was caused by the difference in the wavelength and incidence angle of the laser light. The analysis 9 of the light-intensity change indicated that the change of the sample state occurred in the following sequence: glass (LDG or HDG), supercooled liquid (SCL), crystal (cryst), and liquid (L) states as indicated by the symbols inserted in Figure 2.…”