Birefringence-temperature relations

Figure 8. Representative birefringence-temperature relations for the 220-18,500 PDMS networks. Filled circles locate results obtained to check for reversibility (16).

The addition of water to solutions of PBT dissolved in a strong acid (MSA) causes phase separation in qualitative accord with that predicted by the lattice model of Flory (17). In particular, with the addition of a sufficient amount of water the phase separation produces a state that appears to be a mixture of a concentrated ordered phase and a dilute disordered phase. If the amount of water has not led to deprotonation (marked by a color change) then the birefringent ordered phase may be reversibly transformed to an isotropic disordered phase by increased temperature. This behavior is in accord with phase separation in the wide biphasic gap predicted theoretically (e.g., see Figure 8). The phase separation appears to occur spinodally, with the formation of an ordered, concentrated phase that would exist with a fibrillar morphology. This tendency may be related to the appearance of fibrillar morphology in fibers and films of such polymers prepared by solution processing. 

From electric birefringence measurements it was concluded that the proteins are ordered head-to-tail within the fibril, in a helical configuration (Rogers et al. 2005). The fact that one needs a minimal temperature in order to induce fibrillisation is directly related to the fact that at a certain elevated temperature the protein will partially unfold. Since we have also observed the formation of fibrils at 4°C, after having applied this (partial) denaturation step, the elevated temperature is not essential during assembly. However, at the lower temperature, the assembly was found to be much slower, indicating that temperature affects the kinetics of the assembly process. The relation between the fibrillar type of assembly and the partially unfolded state also has been found for other proteins (e.g., ovalbumin, hen egg white... 

Fig. 11.5 The relation between birefringence and stress for natural rubber at various temperatures , strain increasing and O, strain decreasing. Data for the various temperatures are offset along the birefringence axis. (Reproduced by permission of the Royal Society of Chemistry.)...

FIGURE 3.34 Relation between birefringence and take-up velocity at various extrusion and cooling air temperatures for polypropylene. (From Shimizu, J. Toriumi, K. Imai, Y. Sen-i Gakkaishi, WTl, 33, T-255. With permission.)... 

---