Brillouin scattering study of hypersonic relaxation in a Ca(NO3)2–KNO3mixture

Acoustic Anomalies and Fast Relaxation Dynamics of Amorphous Progesterone as Revealed by Brillouin Light Scattering

The amorphous state of pharmaceuticals has attracted much attention due to its high bioavailability and other advantages. The stability of the amorphous state in relation with the local molecular mobility is important from both fundamental and practical points of view. The acoustic properties of amorphous progesterone, one of the representative steroid hormones, were investigated by using a Brillouin inelastic light scattering technique. The Brillouin spectrum of the longitudinal acoustic mode exhibited distinct changes at the glass transition and the cold-crystallization temperatures. The acoustic dispersions of the longitudinal sound velocity and the acoustic absorption coefficient were attributed to the fast and possibly the secondary relaxation processes in the glassy and supercooled liquid states, while the structural relaxation process was considered as the dominant origin for the significant acoustic damping observed even in the liquid phase. The persisting acoustic dispersion in the liquid state was attributed to the single-molecule nature of the progesterone which does not exhibit hydrogen bonds in the condensed states.

Fast and slow components in the crystallization of a model multicomponent system, NaKCa(NO3): the role of composition fluctuations

We use calorimetrically detected crystal nucleation and growth studies to broaden the discussion of fluctuation-induced nucleation processes to include composition fluctuations in ionic complex-forming systems. We use the model system Ca(NO(3))(2)-KNO(3) with NaNO(3) introduced as a third component, so that crystallization kinetics can be controlled by change of alkali cation at constant mole fraction of Ca(NO(3))(2). At fixed NaNO(3) content, we find separate and thermodynamically anomalous kinetics for the crystallization of NaNO(3) and Ca(NO(3))(2),which we attribute to the importance of slow concentration fluctuations in the latter case. The "nose" of the time-temperature-transformation TTT curve for crystallization of the Ca(NO(3))(2) occurs at much higher temperatures and longer times than that for NaNO(3) and the shape of the curve is different. Above the metastable liquidus surface of NaNO(3), supercooled ternary melts can persist for long times. Suppression of the fast NaNO(3) crystallization, by replacement of Na(+) by K(+), is a prerequisite for easy vitrification in this system.

Strong and Fragile Behavior in Liquid Polymers

In the light of the strong and fragile classification of simple liquids we review some of the relaxation data for some well-known polymers to see the extent to which a similar pattern may be manifested. Relaxation time data rather than viscosity data are used in the polymer case to avoid complications from long chain effects on the Vogel-Fulcher equation pre exponent. A combination of light scattering and 13C NMR data seem to provide the most reliable guide to the microviscosity of interest to the classification. A pattern similar to that for viscous liquids is recovered with polyisobutylene, the “strongest” chain polymer and bisphenol polycarbonate, the most fragile. The extent to which correlations of other properties with fragility, found in the non-polymeric liquids cases, will carry over to the polymer case is still being evaluated, though the work of Hodge on the analysis of the more complicated problem of non-linear thermal relaxation, suggests the carry over may be extensive.