A vapor-deposited cis/trans-decalin mixture glass showed signs of greater stability than the corresponding glass made by cooling the liquid under particular deposition conditions. At a normalized temperature of 0.88 Tg, relative to the glass-transition temperature, the as-deposited mixture had a heat capacity 1.8% lower and an onset temperature 7 K higher than the liquid-cooled glass.
The experiments tested whether stable glasses could be formed from molecular mixtures and highly fragile glassformers.
What the tests compared
Researchers deposited the materials from vapor and measured the resulting glasses with in situ AC nanocalorimetry, a technique that tracks reversing heat capacity. They compared those readings with ordinary glass made by cooling the liquid after the dynamic glass transition.
The mixture tests covered 25/75, 50/50, 75/25 and 100/0 cis/trans-decalin compositions. Heat-capacity differences were expressed as Cp,AD/Cp,OG − 1 at 0.85 Tg, using 119.5 K for cis-decalin and 114.5 K for the 50/50 mixture.
Across the compositions tested, each as-deposited glass had lower heat capacity and a higher onset temperature than its corresponding liquid-cooled glass. The onset temperature was used as an operational measure of kinetic stability: a higher value indicated that the material began to change at a higher temperature.
The temperature window mattered
The advantage was not seen at every deposition temperature. For all the systems investigated, glasses deposited very near Tg had properties identical to those of the corresponding liquid-cooled glasses.
Near the lowest substrate temperatures, the fractional heat-capacity decrease reached 4.5 ± 1% for cis-decalin and 2.5 ± 0.5% for the cis/trans-decalin mixture.
The onset-temperature comparison showed a similar pattern. Between 0.84 and 0.94 Tg, increases reached up to 8 ± 1 K for cis-decalin and 7 ± 1 K for the decalin mixture.
A slow transformation
The researchers also followed the 50/50 mixture during a quasi-isothermal annealing experiment, in which the glass was held at nearly constant temperature. It was deposited at 0.86 Tg, or 115.9 K, and then annealed at 136.6 K.
Under that protocol, the reported transformation took about 43,000 seconds. The figure was obtained by linear extrapolation and was equivalent to 104.4 times the structural relaxation time of the equilibrium supercooled liquid, the reference timescale for rearrangement in that liquid.
A result with clear boundaries
The paper identified the 50/50 cis/trans-decalin mixture as having the highest fragility among molecular glassformers. In this context, fragility describes how sharply a glass-forming liquid's behavior changes with temperature.
The authors concluded that extremely poor glassformers can form stable glasses when mixed with about 25% of a second component.
That conclusion did not apply to every material tested. Attempts to prepare a stable vapor-deposited glass from pure trans-decalin were unsuccessful, with crystallization proposed as the explanation.
The evidence is limited to calorimetric comparisons within the listed cis-decalin and cis/trans-decalin systems. It does not establish that every molecular mixture will form a stable glass.
The study acknowledged funding from the US National Science Foundation and the German Science Foundation.
Paper data and sources
Original title: Highly Stable Glasses of cis-Decalin and cis/trans-Decalin Mixtures
Authors: Katherine R. Whitaker, Daniel J. Scifo, M. D. Ediger et al.
Journal/Repository: J. Phys. Chem. B 2013, 117, 12724-12733
Status: Peer-reviewed
First online: 2026-08-24
DOI: 10.1021/jp400960g
Original paper · Full text