Proton NMR study of CBOOA, NBOOA, and their chain-deuteriated homologues in smectic Ad and nematic mesophases
Titel:
Proton NMR study of CBOOA, NBOOA, and their chain-deuteriated homologues in smectic Ad and nematic mesophases
Auteur:
Miyajima, Seiichi Chiba, Takehiko
Verschenen in:
Liquid crystals
Paginering:
Jaargang 11 (1992) nr. 2 pagina's 283-292
Jaar:
1992-02-01
Inhoud:
The nature of the smectic Ad to nematic phase transition and the modes of molecular motion were investigated for the homologous mesogens, CBOOA, NBOOA, and their chain-deuteriated compounds. In NBOOA, the SAd-N phase transition was found to be first order with a pronounced pretransitional decrease of the orientational order parameter, <P2>, both above and below the transition point, while in CBOOA the anomaly in <P2> was very small. Despite the different behaviours in terms of the orientational order, the dynamical aspects of molecular motion, probed by the-NMR relaxation, are quite similar. The motional mode characteristic of the N phase is order director fluctuation, but translational self-diffusion becomes the dominant relaxation mechanism in the SAd phase. It is also recognized that the relative importance of these mechanisms changes in a continuous manner as a function of temperature.
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