Hiking down the Energy Landscape:  Progress Toward the Kauzmann Temperature via Vapor Deposition

Abstract

Physical vapor deposition was employed to prepare amorphous samples of indomethacin and 1,3,5-(tris)naphthylbenzene. By depositing onto substrates held somewhat below the glass transition temperature and varying the deposition rate from 15 to 0.2 nm/s, glasses with low enthalpies and exceptional kinetic stability were prepared. Glasses with fictive temperatures that are as much as 40 K lower than those prepared by cooling the liquid can be made by vapor deposition. As compared to an ordinary glass, the most stable vapor-deposited samples moved about 40% toward the bottom of the potential energy landscape for amorphous materials. These results support the hypothesis that enhanced surface mobility allows stable glass formation by vapor deposition. A comparison of the enthalpy content of vapor-deposited glasses with aged glasses was used to evaluate the difference between bulk and surface dynamics for indomethacin; the dynamics in the top few nanometers of the glass are about 7 orders of magnitude faster than those in the bulk at Tg - 20 K.

Supercooled liquids with enhanced orientational order

“…In contrast to approaching the glass transition by quenching or pressurizing the liquid, vapour deposition in the glassy state operates in thermodynamic equilibrium, taking advantage of the enhanced molecular mobility at the free surface 23 , where evaporated molecules can rapidly sample the energetic landscape and reach deeper minima before being buried by the upcoming layers. This preparation method thus proves to be, at present, the most efficient way to produce glasses with the lowest thermodynamic excess quantities (enthalpy, volume, entropy) 24 .…”

High Frequency Acoustics in Colloid-Based Meso- and Nanostructures by Spontaneous Brillouin Light Scattering

“…[169] For silicone oil, temperature down-jumps of 1.5 K near T g resulted in a 2.7% increase in the modulus during the 10 4 s equilibration time. [168] Based on calorimetry measurements, [31,175] it was previously estimated that IMC and TNB samples vapor-deposited under the conditions utilized here have properties similar to those expected after aging an ordinary glass for more than 300 years. Thus it is not surprising that aging for hours or days does not produce the large modulus changes reported here.…”

“…These two molecules are well-known glass-formers and their glasses have been previously prepared with physical vapor deposition. [31,174,175] During deposition, the temperature of the substrate T substrate and the deposition rate are the important control parameters. For this work, T substrate was held near 0.85 T g , i.e., 265 K for IMC and room temperature (≈295 K) for TNB.…”

“…It has previously been shown that these deposition conditions produce glasses with low enthalpy, high density, and high kinetic stability. [31,[174][175][176][177] T substrate was controlled by attaching the SiO 2 substrates to a copper temperature stage (Fig. 6.1a).…”

“…A characteristic kink in the temperature-dependent phase velocity indicates T g and the value obtained is in reasonable agreement with the value obtained from differential scanning calorimetry. [174,175] From the phase velocities c l,t in Fig. 6.2, the moduli of the stable glass and the ordinary glass can be calculated.…”