Vapor-Deposited Ethylbenzene Glasses Approach “Ideal Glass” Density

Abstract

Spectroscopic ellipsometry was used to characterize vapor-deposited glasses of ethylbenzene (T g = 115.7 K). For this system, previous calorimetric experiments have established that a transition to the ideal glass state is expected to occur near 101 K (the Kauzmann temperature, T K) if the low-temperature supercooled liquid has the properties expected based upon extrapolation from above T g. Ethylbenzene glasses were vapor-deposited at substrate temperatures between 100 (∼0.86 T g) and 116 K (∼T g), using deposition rates of 0.02–2.1 nm/s. Down to 103 K, glasses prepared in the limit of low deposition rate have densities consistent with the extrapolated supercooled liquid. The highest density glass is within 0.15% of the density expected for the ideal glass. These results support the hypothesis that the extrapolated properties of supercooled ethylbenzene are correct to within just a few Kelvin of T K, consistent with the existence of a phase transition to an ideal glass state at T K.

Glasses denser than the supercooled liquid

“…Close to the nominal Tg (bulk), the density of the as-deposited films can reach this limiting value, while at lower T dep , the system is kinetically trapped with ∆ρ < ∆ρ (SCL). This observation is similar to the previous reports in stable glasses of TPD and other molecules (7,16,33,39).…”

“…After the molecules are buried deeper into the film, their relaxation dynamics significantly slow down, which prevents further equilibration. Through this surface-mediated equilibration process, stable glasses can achieve low-energy states on the potential energy landscape that would otherwise require thousands or millions of years of physical aging (2,3,15,16).…”

“…The Kauzmann crisis occurs at the Kauzmann temperature (TK), where the extrapolated SCL has the same structural entropy as the crystal, producing thermodynamically impossible states just below this temperature. Recently, Beasley et al (16) showed that nearequilibrium states of ethylbenzene can be produced using PVD down to 2 K above TK and hypothesized that any phase transition to an "ideal glass" state to avoid the Kauzmann crisis must occur at TK.…”

Dielectric properties of vapor-deposited propylbenzenes

“…10 Apart from possible PVD induced anisotropy effects, the properties of asdeposited films are similar to what is expected from glasses prepared by ordinary cooling and after aging times of thousands or millions of years. 5,11,12 The feature made responsible for the unusual and interesting properties of PVD films is the combination of a low temperature (and thus strong driving force towards low energy states) with the relatively high surface mobility, 13 which allows newly arrived molecules to sample a large parameter space during deposition. 10 As the local environment at the surface dominates the arrest of molecules for sufficiently low deposition rates, the difference between glasses obtained by vapor deposition and ordinary cooling may depend on the intermolecular interactions.…”

Reaching the Ideal Glass in Polymer Spheres: Thermodynamics and Vibrational Density of States

“…The existence of a supercooled liquid below T K would imply an entropy catastrophe with the unphysical scenario of a liquid having smaller entropy than that of the corresponding crystal. To avoid this paradoxical scenario, it has been proposed [4][5][6] and largely debated [7][8][9][10][11][12][13][14], that a true second order thermodynamic transition, the so-called "ideal" glass transition, at T K would take place. The existence of such a transition would mean the emergence of an ideal glass residing at the bottom of Goldstein's free energy landscape [15], excluding the crystal occupying the ultimate minimum (see Fig.…”