Stable glasses of indomethacin and α,α,β-tris-naphthylbenzene transform into ordinary supercooled liquids

Abstract

Secondary ion mass spectrometry has been used to characterize translational motion in vapor-deposited glasses of indomethacin (IMC) and α,α,β-tris-naphthylbenzene (TNB). Vapor deposition onto substrates at ∼0.99 T(g) produced ordinary glasses that evolve according to fickian diffusion during annealing. The resulting self-diffusion coefficients for the supercooled liquids are in good agreement with previous reports. Deposition onto substrates at 0.85 T(g) produced highly stable glasses that transform with a propagating front mechanism. In contrast to previous reports, the liquid produced by this transformation has the same translational mobility as the ordinary supercooled liquid; we associate this result with lower impurity levels in the current samples. The front velocities for both TNB and IMC stable glasses are very similar functions of the translational self-diffusion coefficients of the supercooled liquids, consistent with view that the growth front velocity is controlled by mobility in the liquid adjacent to the stable glass.