Unusual Transformation of Mixed Isomer Decahydroisoquinoline Stable Glasses

Dielectric relaxation was used to characterize the ability of vapor-deposited mixtures of cis- and trans-decahydroisoquinoline (DHIQ) to form glasses with a high kinetic stability. Vapor-deposited mixtures are technologically relevant, and the effect of mixing on glass stability is a relatively unexplored area. Mixed isomers and pure trans-DHIQ form highly stable glasses that isothermally transform in approximately 10⁴ τ_α (where τ_α is the structural relaxation time of the supercooled liquid). Isomeric composition of the glasses does not play a significant role in the maximum kinetic stability of the resulting films. Secondary relaxations in DHIQ are associated with an intramolecular conformational change and are suppressed to a significant extent in highly stable glasses. During isothermal annealing experiments, stable glasses were found to transform initially via a growth front mechanism that transitions to a homogeneous bulk mechanism. Surprisingly, the time dependence of the bulk transformation is different from that reported for other stable glasses and cannot be interpreted in terms of a simple nucleation and growth model.