Highly stable glasses of cis-decalin and cis/trans-decalin mixtures.

In situ AC nanocalorimetry was used to measure the reversing heat capacity of vapor-deposited glasses of decahydronaphthalene (decalin). Glasses with low heat capacity and high kinetic stability, as compared to the corresponding liquid-cooled glass, were prepared from cis-decalin and from several cis/trans-decalin mixtures. This is the first report of highly stable glass formation for molecular mixtures. The 50/50 cis/trans-decalin mixture is the highest fragility material reported to produce an ultrastable glass. The 50/50 mixture exhibited high kinetic stability, with a ∼500 nm film deposited at 116 K (0.86 Tg) displaying a transformation time equivalent to 10(4.4) times the structural relaxation time of the supercooled liquid at the annealing temperature. cis-Decalin and the decalin mixture formed stable glasses that had heat capacities as much as 4.5% lower than the liquid-cooled glass.