Temperature zero mobility

Hatley and Blair [3.69] presented mean Tg data for anhydrous carbohydrates (Table 3.1), which vary in the literature owing to measurement and interpretation differences. Small amounts of water may depress the data substantially. The physical stability of amorphous formulations below Tg is generally accepted, and a collapse can be avoided. This does not always apply to the chemical stability. If the temperature is reduced below T, the configurational entropy diminishes until it reaches zero. This T0 (also shown in Table 3.1) is called the zero mobility temperature at which the molecular motion stops. The authors define three areas of chemical reactions above Tg, chemical reactions are generally possible at T, reactions such as aggregation, which require substantial molecular motion, stop and between Tg and T0, reactions involv-... 

Is the Hydration Limit Related to the Zero Mobility Temperature .307... 

Chapter 9. For hole transport in PDA doped PCZ, the mobilities were field dependent, varying as logp < The zero-field temperature dependencies... 

Borsenberger and Rossi (1992) measured electron mobilities of 30% 3,3 -dimethyl-5,5 -di-f-butyl-diphenoquinone and 3,5 -dimethyl-3,5-di-/-butyl-diphenoquinone (DPQ) doped into PS and PC. The field and zero-field temperature dependencies were described as logp El/2 and -(T0IT)2. Figure 8 shows the room temperature field dependencies. As reported for a number of... 

Though there have been significant advances in the sophistication of longterm stability predictions (i.e., beyond a simple Tg-based approach), the hydration limit continues to be an active area of research in our and others laboratories. The hydration limit may be related to the temperature of "zero mobility" and that the use of the temperature dependence of the hydration limit has shovm some promise as a quantitative approach to determine the effect of residual water on the long-term stability of amorphous solids. 

Here 7J, is a new nonzero vanishing mobility temperature that is characteristic of each liquid and lies far below the temperature at which each diffusivity plot in Fig. 3 tends to zero on the linear scale. The claim of to physical significance is that it falls below the observed normal 7, such that 7 1.1 to 1.3 Tq and is usually coincident with the temperature at which the supercooled liquid entropy, measured below the fusion temperature, extrapolates to the same value as for the crystal (though the free energy of the latter remains lower Equation 5 implies an apparent activation energy that varies with temperature according to... 

The temperature of zero mobility. To, correlates well with the calorimetric glass temperature Tg, where T g=(T o+20 K). 

From a knowledge of the crystal-melting temperature, I m, the glass temperature can be estimated with some degree of conhdence, at least for many of the excipients commonly used for freeze-dried pharmaceutical preparations, where it has been found empirically that Fg/rm 0.73. Furthermore, for the same preparations, the temperature of zero mobility can be approximated by Fm/2. Also, for many materials, ACgTg x 100 kJ g At T , the viscosity of most glasses is assumed to lie between... 

In agreement with the Williams-Landell-Ferry (WLF) theory, the translational mobility of macromolecular segments fully disappears, due to diminishing free volume which reaches zero at temperature To < Tg. For this theory, the following expression is valid ... 

As we continue lowering the pressure, GC is the final limiting case when the mobile phase has zero solvent strength over the entire column length and where temperature is the only effective control parameter. Gas chromatography is shown in Figure 7.3. 

Figure 12-25. The temperature dependencies of die zero-field mobility for TTA and TTA doped wilh DTA, DAT, and TAA. The TTA concentration was 40%, ihe hinder material was polystyrene. The DTA, DAT and TAA to TTA concemialiinis were 1.11x10 5 niol/niol TIA (Ref. 7(> ).

We note a temperature dependence of the zero field mobility as exp[—( F()/F)2], a behavior which is indeed encountered in real organic semiconductors, and differs from both Millers-Abrahams fixed range and Moll s variable range hopping models. 

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