Thermal randomization analysis curve

Water-soluble random copolymers containing u-phenylalanine and A -O-hydroxypropylR-glutamine are prepared. The thermally induced helix-coil transition in these copolymers in water is studied. The incorporation of (.-phenylalanine is found to increase the helix-content of the host polymer. The Zimm-Bragg parameters cr and s for the helix-coil transition in poly(L-phenylaianine) in water are deduced from an analysis of the melting curves of the copolymers. The values of s, computed from both the Lifson and Allegra theories are (Ufson/Allegra a 0.0018) s 1.056/1.061 (273 K), 1.078/1,086 (293 K), 1.041/1.047 (313 K), 1.000/1.003 (333 K). 

Fig. 7 illustrates Chapman s treatment of the mechanics of this composite system. The system is treated as a set of zones consisting of fibril and matrix elements. Originally, this was introduced as a way of simplifying the analysis, but, the later identification of the links through IF protein tails makes it a more realistic model than continuous coupling of fibrils and matrix. Up to 2% extension, most of the tension is taken by the fibrils, but, when the critical stress is reached, the IF in one zone, which will be selected due to statistical variability or random thermal vibration, opens from a to P form. Stress, which reduces to the equilibrium value in the IF, is transferred to the associated matrix. Between 2% and 30% extension, zones continue to open. Above 30%, all zones have opened and further extension increases the stress on the matrix. In recovery, there is no critical phenomenon, so that all zones contract uniformly until the initial extension curve is joined. The predicted stress-strain curve is shown by the thick line marked with aiTows in Fig. 6b. With an appropriate. set of input parameters, for most of which there is independent support, the predicted response agrees well with the experimental curves in Fig. 6a. The main difference is that there is a finite slope in the yield region, but this is explained by variability along the fibre. The C/H model can be extended to cover other aspects of the tensile properties of wool, such as the influence of humidity, time dependence and setting.

On differential thermal curves for vermiculites and saponites, as already mentioned, a small endothermic peak can occur at about 600°C associated with a small exothermic peak at 800 to 900°C. This normally indicates the interstratification of some brucite layers (see Figure 20), but these are frequently so few (or incomplete) and so randomly interstratified that their presence is not revealed on the X-ray pattern. Differential thermal analysis is, therefore, a particularly sensitive method of detection. 

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