Entropic region

In another study, thermodynamic parameters have been investigated with a tris(4-methyIbenzoate)-derivatized cellulose type CSP (Chiralcel OJ) and a chiral diol compound. It was found that at low temperatures, the enantioselectivity is entropy-driven (region 11), while at higher temperatures the separation is enthalpy-driven (region 1) (see Fig. 9.8). DSC and IR experiments revealed that the transitions between the enthalpic and the entropic regions of the van t Hoff plots are a result of a change in conformation of the stationary phase [76]. 

As explained in the Appendix 10. A, G lo) spectra are intrinsically not suitable for testing the validity of the ERT or the Rouse theory if the line-shape analyses are to cover only the entropic region. 

Appendix lO.A — The Reason Why G"(u ) Should Be Excluded from the Line-Shape Analysis in Terms of the Rouse Theory or the ERT If Only the Entropic Region Is to Be Covered... 

The energetic region has rarely been studied for two reasons one experimental and the other theoretical. Experimentally, accurate measurements of G t) or G u>) over the energetic region require an extremely stiff transducer, which, due to lack of enough sensitivity, is in general not suitable for the commonly studied entropic region. For this reason, the experimental G t) and G u>) results studied in Chapters 10 and 11 are confined to the... 

With the ERT and the Rouse theory successfully applied to the entropic region, J t) line shapes over the whole time range have been quantitatively analyzed in a systematic way as the KWW form for the glassy relaxation... 

The successful application of the ERT to the entropic region of the viscoelastic response of entangled systems has been shown by extensive analyses of the G t) and G (jj) results (Chapter 10). As expected from this, the J t) line shape (at a certain temperatme) of an entangled sample over the... 

Fig. 14.10 The viscoelastic spectra G (cj) of LIO measured at different temperatures (V at 92°C A at 95°C O at 99°C at 105°C A at 110°C at 120°C and at 130° C) composed together by matching all the spectra over the glassy-relaxation region (using 105° C (AT = 15K) as the reference temperature) and superimposed on the corresponding calculated curves (the glassy-relaxation region solid line the entropic region solid line at 105°C (AT = 15K), long-dash line at 110°C (AT = 20K), medium-dash line at 120°C (AT = 30K), and short-dash line at 130°C (AT = 40K)).

---