earticle

영어

The oscillation in the entropy change at the NI(nematic-isotropic) phase transition temperature becomes less distinct when the linking group is replaced by the carbonate. In our previous work, we have suggested that such characteristics arise from the geometrical arrangement of the linkage. In this work, deuterium NMR studies have been carrier out for a series of carbonate-type dimer liquid crystals MCOC(O)O(CH2)OC(O)CN(CBC-c, c=5.6) to elucidate the conformational characteristics of the spacer in the nematic phase. The H-NMR spectra were recorded on a JEOL GSX-500 apparatus by using deuterium labelled CBC-n. Following the previous treatment, the single-ordering-matrix model was adopted, in which the molecular axis was defined along the line connecting the centers of the terminal mesogenic cores. Conformer fractions were estimated by simulation so as to reproduce the observed NMR profile. Under a nematic constraint the conformers should be restricted to a certain portion of all the allowed conformations of the spacer in the free stats. Hence the calculations were carried out for an ensemble of conformer having the angle between the mesogenic core and the molecular axis smaller than a certain valur Successful results were as follows: