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Title: Unique Pitch Evolution in the Smectic -C-alpha* Phase

Abstract

Employing resonant x-ray diffraction, we observed unique pitch evolutions in the smectic-C{alpha}* phase in mixtures of two antiferroelectric liquid crystals. Our results show that the pitch in this phase continuously evolves across 4 layers, contradicting a theoretical model that predicts that the smectic-C{sub FI2}* phase intervenes in the smectic-C{alpha}* phase. The phase sequences we found can be explained by another model that includes one type of long-range interaction among smectic layers.

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930521
Report Number(s):
BNL-80520-2008-JA
Journal ID: ISSN 0031-9007; PRLTAO; TRN: US200904%%764
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review Letters; Journal Volume: 99; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ANTIFERROELECTRIC MATERIALS; INTERACTION RANGE; LIQUID CRYSTALS; MIXTURES; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Liu,Z., McCoy, B., Wang, S., Pindak, R., Caliebe, W., Barois, P., Fernandes, P., Nguyen, H., Hsu, C., and Wang, . Unique Pitch Evolution in the Smectic -C-alpha* Phase. United States: N. p., 2007. Web. doi:10.1103/PhysRevLett.99.077802.
Liu,Z., McCoy, B., Wang, S., Pindak, R., Caliebe, W., Barois, P., Fernandes, P., Nguyen, H., Hsu, C., & Wang, . Unique Pitch Evolution in the Smectic -C-alpha* Phase. United States. doi:10.1103/PhysRevLett.99.077802.
Liu,Z., McCoy, B., Wang, S., Pindak, R., Caliebe, W., Barois, P., Fernandes, P., Nguyen, H., Hsu, C., and Wang, . Mon . "Unique Pitch Evolution in the Smectic -C-alpha* Phase". United States. doi:10.1103/PhysRevLett.99.077802.
@article{osti_930521,
title = {Unique Pitch Evolution in the Smectic -C-alpha* Phase},
author = {Liu,Z. and McCoy, B. and Wang, S. and Pindak, R. and Caliebe, W. and Barois, P. and Fernandes, P. and Nguyen, H. and Hsu, C. and Wang, .},
abstractNote = {Employing resonant x-ray diffraction, we observed unique pitch evolutions in the smectic-C{alpha}* phase in mixtures of two antiferroelectric liquid crystals. Our results show that the pitch in this phase continuously evolves across 4 layers, contradicting a theoretical model that predicts that the smectic-C{sub FI2}* phase intervenes in the smectic-C{alpha}* phase. The phase sequences we found can be explained by another model that includes one type of long-range interaction among smectic layers.},
doi = {10.1103/PhysRevLett.99.077802},
journal = {Physical Review Letters},
number = 7,
volume = 99,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • We have investigated the smectic-C*{sub {alpha}}-smectic-C* (SmC*{sub {alpha}}-SmC*) transition in a series of binary mixtures with resonant x-ray diffraction, differential optical reflectivity, and heat capacity measurements. Results show that the phases are separated by a first-order transition that ends at a critical point. We report the observation of such a critical point. We have proposed the appropriate order parameter and obtained values of two critical exponents associated with this transition. The values of the critical exponents suggest that long-range intersections are present in the SmC*{sub {alpha}}-SmC* critical regions.
  • The layer structure of the smectic-C{sub {alpha}}{sup *} phase of one liquid-crystal compound has been acquired from both differential optical reflectivity and ellipsometry measurements in the free-standing film geometry. The data from both techniques display characteristic oscillations as a function of temperature, which can be described by a model for the film consisting of surface anticlinic layers and an interior short-pitched azimuthal helix. These results are consistent with those found previously for another compound. Depolarized reflected light microscopy is used to study the films when the unique features of the aforementioned oscillations occur.
  • The smectic C*-alpha (SmC{sub α}*) phase is one of the sub-phases of ferroelectric liquid crystals that has drawn much interest due to its electro-optical properties and ultrafast switching. Generally observed above the ferroelectric SmC* phase in temperature, the SmC{sub α}* commonly shows only very narrow phase temperature range of a few degree Celsius. To broaden the SmC{sub α}* phase, polymer stabilization was investigated for thermal phase stabilization. Two different reactive monomers were tested in three mixtures, and all three broadened the temperature range of the SmC{sub α}* phase from 3 °C to 39 °C. The current reversal method was used to determinemore » the phase existence versus temperature. Moreover, the texture and network structure was studied by polarized optical microscopy and scanning electron microscopy, with the latter revealing the confinement of the smectic layer structure within the porous polymer network.« less
  • Experimentally high-resolution ac calorimetry measurments on a liquid-crystal compound exhibiting a smectic-A - smectic-C (SmA-SmC) phase transition which is shown to be mean-field-like is presented. In the light of this experimental result, a simple and convincing argument, based on the mean-field theory, is given to explain why non-mean-field critical exponents were obtained in many of the studies on the SmA-SmC transition. The theory not only gives an excellent fit to the data for temperatures below the transition temperature but also provides a qualitative prediction on the size of the deviation from the linear relationship between (T/sub c/-T) and the squaremore » of the order parameter. The predicted deviation is consistent with x-ray measurements on the order parameter of another liquid-crystal compound.« less