Self-Diffusion of Supercooled Tris-naphthylbenzene

Anisotropic structure and transformation kinetics of vapor-deposited indomethacin glasses

One- and two-dimensional wide-angle X-ray scattering (1D and 2D WAXS) measurements were performed on vapor-deposited glasses of indomethacin. Physical vapor deposition can be used to prepare organic glasses with high kinetic stability and other properties that are expected for glasses that have been aged for thousands of years. It was previously reported that 1D WAXS from such stable glasses contains an extra peak at q = 0.6 Å(-1) that is not characteristic of the ordinary glass or expected for a highly aged glass. 2D WAXS measurements presented here show that the extra WAXS peak is caused by anisotropic packing in the vapor-deposited glass. The electron density is modulated normal to the film surface with a period roughly equal to the center of mass separation of indomethacin molecules. When such samples are annealed, the packing in the sample becomes isotropic. The transformation time for this process is much longer than the structural relaxation of the supercooled liquid and has a weaker temperature dependence. The observed temperature dependence of the transformation time is consistent with a growth front mechanism for the conversion of the stable glass into the supercooled liquid.

Dynamic arrest in multicomponent glass-forming alloys

We report radiotracer diffusivities in a Pd43Cu27Ni10P20 melt, presenting for the first time a complete set of data for all components over the whole relevant temperature range. While a vast decoupling of more than 4 orders of magnitude is observed between the diffusivity of Pd and of the smaller components, at the glass transition temperature Tg, the diffusivities of all components merge close to the critical temperature Tc of mode coupling theory. For Pd, the Stokes-Einstein relation holds in the whole range investigated encompassing more than 14 orders of magnitude suggesting the formation of a slow subsystem as a key to glass formation in systems with dynamic asymmetry.

Using rare gas permeation to probe methanol diffusion near the glass transition temperature

The permeation of rare-gas atoms through deeply supercooled metastable liquid methanol films is used to probe the diffusivity. The technique allows for measurement of supercooled liquid mobility at temperatures near the glass transition. The temperature dependence of the diffusivity is well described by a Vogel-Fulcher-Tamman equation. These new measurements and the temperature dependent kinetic parameters obtained from their analysis provide clear evidence that methanol is a fragile liquid near the glass transition.