Demixing temperature

Fig. 2 Typical thermogram obtained using conventional differential scanning calorimetry on PNIPAM solution the temperature of maximum heat capacity (Tmax), the width of the transition at half-height (AT1/2), the heat of transition (AH), the difference in the heat capacity before and after the transition (ACp), and the demixing temperature (Tdem). (Adapted from Ref. [200])...

The course of the elaidinization reaction can be followed graphically by means of the critical demixing temperature of the oil, using, for example, aniline as a solvent. According to Dahmen the rise in the critical demixing temperature is approximately proportional to the degree of elaidinization (cf. Fig. 85). 

In Fig. 85 the critical demixing temperature of isomerized olive is plotted against the percentage of elaidinized oil (calculated on the amount of elaidinic acid that can... 

Fig. 85. Elaidinization of olive oil. Critical demixing temperatures /od p cl ted against...

The course of the elaidinization reaction can be followed by dilatometric measurements (11), consistency determinations (12), by means of critical demixing temperatures, using aniline or triacetin as a solvent (9), or, more directly, by infrared spectrophotometry (13). 

Figure 4. Demixing temperatures for Lennard-Jones polymer in Lennard-Jones solvent at P, = 2 as a function of polymer concentration for 16-mers (circles) and 64-mers (triangles). Temperature and pressure units are relative to the critical solvent properties. The Lennard-Jones interaction potential energy is cut at 2.5a and shifted [80].

Chu and co-workers (IJO, 111) have studied the photon correlation function of light scattered by solutions of narrow molecular weight fractions of PS (Mn = 397,000) in cyclohexane near the critical demixing temperature Tc- Their data fit Equations 82 and 83 with y = 1.26 0.08, y = 0.77. The correlation lengths were in the range of 100-250A, and Vs = 0.62, vr = 0.58. For (T — Tc) < 0.1°, deviations from the critical exponent concept were discovered which may result from macro-molecular polydispersity or configurational fluctuations 111)-... 

When the compositions of both the organic phase and the water phase change strongly with temperature (the middle part of the phase line), points on the liquid-liquid phase line are most reliably determined by using the first method (accuracy 0.05 °C). However, when the mixing/demixing temperature is a very strong function of the amine to water ratio in the mixture (the sides of the phase line), the second method is favoured for maximum reliability. 

Figure 6-12. Schematic representation of the molar Gibbs energy (above) and the demixing temperature (below) as a function of the volume fraction of the solute for a partially miscible system, st. Stable region m, metastable region u, instable region b, binodals, sp, spinodals Ti, temperature for which the upper diagram is applicable.

The difference between the volume fraction of the solute at the maximum of the cloud-point curve and the critical volume fraction can be used as a measure of the polymolecularity. The same holds for the difference between the maximum cloud-point temperature and the critical demixing temperature. 

Fig. 14. B, average number of broken bonds per chain (Eq. (38)) vs. degradation time in the presence of two different radical scavengers at a shear rate of 10800 s . Uo denotes the starting molecular nonuniformity (= P. o/P ,o — 1) and AT is the distance to the demixing temperature...

At present, the most plausible explanation may be sought in the alterations of solvent quality by DPPH through preferential adsorption onto the chains. This would lead to an improvement of solvent qualitj and the results obtained in the presence of DPPH may be compared with those obtained using at a greater distance to the demixing temperature. A more detailed discussion of this point is given in Sect. 6.6 when considering the influence of AT. 

Fig. 20. Influence of shear rate initial rate of degradation (dB/dtX=o vs. shear rate for polystyrene dissolved in-trons-decalin AT denotes the distance to the demixing temperature...

All data have been taken from Ref. Radical scavenger Oj AT is the distance to the demixing temperature (dB/dt),o is the inditial rate of degradation (cf Eq. (42)) is the shear rate and X and R are the parameters characterizing the Gaussian breakage probability (cf Eq. (37))... 

Figure 35-6. Demixing temperatures as a function of composition for mixtures of a poly(isobutylene) with the molar mass 250 g/mol and polyCdimethyl siloxanes) with the molar masses of 850, 1 350, and 17 500 g/mol.

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