Generalized Langevin-Debye model of the field dependence of tilt, birefringence, and polarization current near the de Vries smectic-A* to smectic-C* liquid crystal phase transition.
In chiral smectic-A (Sm-A) liquid crystals, an applied electric field induces a tilt of the optic axis from the layer normal. When these materials are of the de Vries type, the electroclinic tilt susceptibility is unusually large, with the field-induced director reorientation accompanied by a substantial increase in optical birefringence with essentially no change in the smectic layer spacing. In order to account for the observed electro-optic behavior, we assume that the molecular orientation distribution in the Sm-A has two degrees of freedom: azimuthal orientation and tilt of the molecular long axis from the layer normal, with the tilt confined to a narrow range of angles. We present a generalized Langevin-Debye model of the response of this orientational distribution to applied field that gives a field-induced optic axis tilt, birefringence, and polarization dependence that agrees well with experimental measurements and reproduces the double-peaked polarization current response characteristic of a first-order Sm-A(*)-Sm-C(*) transition. Additionally, we find that the measured field-induced polarization and the Langevin-Debye model predictions can be quantitatively described as pre-transitional behavior near the tricritical point of a recently published generalized 3D XY model of interacting hard rods confined to reorient on a cone in the presence of an applied field.
Department of Physics, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Yongqiang
Y
Shen
Department of Chemistry and Biochemistry, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Lixing
L
Wang
Department of Physics, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Renfan
R
Shao
Department of Chemistry and Biochemistry, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Tao
T
Gong
Department of Physics, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Chenhui
C
Zhu
Department of Chemistry and Biochemistry, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Hong
H
Yang
Department of Physics, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Joseph E
JE
Maclennan
Department of Chemistry and Biochemistry, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
David M
DM
Walba
Department of Physics, and the Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA.
Noel A
NA
Clark