Experimental demonstration, using polarized Raman and infrared spectroscopy that both conventional and de Vries smectic_A phase may exist in smectic liquid crystals with a first-order A-C* transition
Citation:
N. Hayashi, T. Kato, A. Kocot, A. Fukuda, J. K. Vij, G. Heppke, S. Kwada, and S. Kondoh, Experimental demonstration, using polarized Raman and infrared spectroscopy that both conventional and de Vries smectic_A phase may exist in smectic liquid crystals with a first-order A-C* transition, Physical Review E, 74, 2006, 051706-1 - 051706-11Download Item:
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Abstract:
Two models exist for the orientational distribution of the long molecular axes in smectic-A liquid crystals:
the conventional unimodal distribution and the ?cone-shaped? de Vries distribution. The de Vries hypothesis
provides a plausible picture of how, at a molecular level, a first-order Sm-A to Sm-C* transition may occur,
especially if there is little or no concomitant shrinkage of the layer spacing. This work investigates two
materials with such transitions: C7 and TSiKN65. The azimuthal distribution of in-layer directors is probed
using IR and polarized Raman spectroscopy, which allows us to obtain orientational order parameters. In
C7, we observe a discontinuous change in the order parameter, the magnitude of which is small compared with
the corresponding change in the in-layer director tilt angle . Assuming that the smectic-A liquid crystal is of
the de Vries type, we calculate the required to reproduce the apparent order parameter P2 app, obtained from
IR, by using the true order parameter P2 , obtained from polarized Raman scattering. The results indicate that,
for C7, the tilt angle so calculated is much smaller than that in the Sm-C* angle and hence de Vries behavior
may not be the appropriate explanation in this case. Conversely, we find that TSiKN65 shows a different
behavior to C7, which can be explained in terms of the de Vries concept. Thus, we conclude that either type of
distribution may exist in Sm-A phases which undergo a first-order transition to the Sm-C* phase. We also
discuss the changes in the smectic layer spacing and the orientational order parameters across the Sm-ASm-
C* phase transition, together with changes in birefringence with applied electric field.
Sponsor
Grant Number
Science Foundation Ireland (SFI)
Author's Homepage:
http://people.tcd.ie/jvijhttp://people.tcd.ie/atsuof
Description:
PUBLISHED
Author: VIJ, JAGDISH; FUKUDA, ATSUO
Type of material:
Journal ArticleSeries/Report no:
Physical Review E74
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Full text availableKeywords:
Electronic & Electrical EngineeringDOI:
http://dx.doi.org/10.1103/PhysRevE.74.051706Licences: