Cooling rate, glassy solids

It is clear that the nematic phase exhibits a featureless Rayleigh wing and that several distinct solid phases can be formed depending on cooling rate [79]. This includes an apparently glassy phase. The vertical tick marks indicate the calculated frequencies of vibrational modes as obtained from density functional methods. 

Metastable alloys, formed by rapid quenching, may be produced as metastable or nonequilibrium solids that are either glassy or microcrystalline. Because of the required cooling rates (106 K/sec)... 

Their second and main concern was the effect of the glass formation history on physical properties. We illustrate this by examining the effect of cooling rate on Tg and the glassy volume. The basic idea is sketched in Figure 4.7, where the free volume is plotted as a function of time. The solid line represents the equilibrium volumes, as... 

FIGURE 4.7 Effect of cooling rate on and the glassy volume. Shown is free volume versus temperature for (a) slow cooling and (b) faster cooling. Solid lines represent equilibrium, from a stepwise reduction of temperature. Dashed lines depict schematically the trend of experimental behavior. (Adapted from Vleeshouwers [1993].)... 

Another important factor in immiscible PLC + EP blends is whether the crystallizing EP phase is crystallizing in the presence of a solid (glassy, crystalline) or flexible (liquid crystalline) PLC phase and this can be assessed by looking at the various crystallization temperatures of PLCs and the EPs (preferably at cooling rates relevant to the processing technique) with which they are blended. This can be... 

In contrast, there are no solvents used in HME processes for manufacturing amorphous solid dispersions. Instead, the mixture of crystalline drug and polymer are heated to a temperature at which the components melt or form a eutectic, and then flash cooled, resulting in a dense amorphous glassy solid. The solid is then milled to achieve uniform particle size distribution, which is then processed into the final formulation. Therefore, the milling step will determine particle size and surface area, which in turn is related to the dissolution rate of the solid. 

The definition and determination of Tg given above in terms of cooling from an equilibrium state at any given q is only one among several other alternative methods to be described below. For workers on viscoelastic liquids who are not interested in the glassy solid state, the value of Tg obtained in this way for a standardized cooling rate is the most appropriate parameter for considering the temperature dependences... 

---