The effect of electric and magnetic fields on the melt organization of a nematic cyclic siloxane liquid crystal
作者:
S.G. McNamee,
T.J. Bunning,
S.S. Patnaik,
C.M. McHugh,
C.K. Ober,
W.W. Adams,
期刊:
Liquid Crystals
(Taylor Available online 1995)
卷期:
Volume 18,
issue 5
页码: 787-794
ISSN:0267-8292
年代: 1995
DOI:10.1080/02678299508036691
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
The presence of periodic diffuse meridional reflections in the X-ray diffraction pattern of the nematic phase of a pentamethylcyclosiloxane compound with pendant mesogenic groups is examined as a function of temperature and frequency of an applied electric field. These reflections are thought to be caused by a tendency of the mesogens to pack in columns of molecules that have no side-to-side registry (uncorrelated strings). Column lengths obtained from the intercepts of plots of δs2versuss2, wheresis the scattering vector and δsis the width of the reflection, indicate association of 3–6 mesogens depending on temperature and frequency. The length over which the strings are correlated are compared to values obtained from a magnetically aligned sample quenched into a glassy nematic phase. The development of a pseudo-layered packing arrangement with decreasing temperature is also discussed. The appearance of a symmetric 4-spot pattern at temperatures slightly above the crystallization temperature suggests the formation of layered domains with local ordering similar to smectic C packing. Layer correlation lengths are calculated and compared for the electrically (110 Å) and magnetically (180 Å) aligned samples.
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