Trans conformations, ratio gauche

With all-atom simulations the locations of the hydrogen atoms are known and so the order parameters can be calculated directly. Another structural property of interest is the ratio of trans conformations to gauche conformations for the CH2—CH2 bonds in the hydrocarbon tail. The trans gauche ratio can be estimated using a variety of experimental techniques such as Raman, infrared and NMR spectroscopy. 

Looked at in a different way, the orientation of gauche conformations is always very low, and the oriented chains are predominantly in the trans conformation so that the increase in the trans/gauche ratio is accompanied by a rapid rise in trans orientation. In fact, it has been pointed out 27) that to a very good approximation the overall orientation... 

The authors prefered the latter explanation. They argue that the difference in the dielectric constant of the medium, when a hydrocarbon rich mixture is compared with that rich in sulfur dioxide, affects the ratio of gauche to trans conformations of the polymer chain. Such effects were observed in other systems, e.g. in 1,2 dichloroethane (38). Hence,... 

The short-range interactions, as shown above, are important in determining the relative probabilities of existence of different conformations in a polymer chain. Thus the ratio of the number of trans nt) to gauche (rig) states is given by... 

The FTIR spectroscopy studies on PTT (refer Figure 9) subjected to isothermal ciystallization for 40 min at 200"C, shows the following result. The area ratio of the absorption band which is assigned to the % of gauche conformation, is calculated to be 1.39 while the ratio which denotes the trans conformation of the methylene groups is found to be 0.28, indicating reasonable amount of crystallinity in the sample (refer Table 8). The crystallinity estimated by DSC analysis after isothermal crystallization at 200°C for 40 min shows a value of 40.8%. ... 

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