Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants

H.S. Chang, S. Jaradat, H.F. Gleeson, I. Dierking, M.A. Osipov, Samsung Electronics Co. (Funder)

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

A series of mixtures comprising an antiferroelectric liquid-crystal host and a chiral dopant is described in which the layer spacing variation at the orthogonal smectic-A* (SmA*) to tilted smectic-C* or smectic-C-alpha* (SmC* or SmC alpha*) phase transition changes from the usual strong contraction in the pure system to one in which there is almost no layer spacing change observed across the transition for dopant concentrations of 7%. The nature of the orthogonal to tilted phase transition is examined using Raman spectroscopy, to determine the order parameters < P-2 > and < P-4 > in the SmA* phase, and via a generalized Landau expansion to reveal the details of the phase transition itself. The results show that the value of < P-2 > at the orthogonal to tilted transition increases from around 0.6 to 0.7 as the dopant concentration increases, while < P-4 > remains constant at approximately 0.4 irrespective of dopant concentration. Further, the generalized Landau potential measurements prove that the transition is purely second order, while electro-optic measurements confirm that the tilt angle at the transition becomes smaller with increasing dopant concentration. The combined data show that the high-temperature tilted phase regime corresponds to a SmC alpha* phase rather than the mechanism suggested by de Vries that is inferred by the layer spacing data alone. We demonstrate that the lower-temperature SmC alpha*-SmC* phase transition is of first order. Further, the temperature range of the SmC alpha* phase increases dramatically with concentration, from around 2 K in the pure system to around 21 K in the 8% doped mixture, showing that the chiral dopant plays a role in stabilizing this phase. Indeed, we particularly note that for the 8% doped mixture all other SmC*-like phases disappear and that the only tilted phase remaining is SmC alpha*. This implies that we are reporting a liquid-crystalline phase sequence, namely, cryst.-SmC alpha*-SmA*-iso., i.e., a direct transition between the SmC alpha* phase and the crystalline phase.
LanguageEnglish
JournalPhysical Review E
Volume79
Issue number6
DOIs
Publication statusPublished - Jun 2009

Fingerprint

Stabilization
stabilization
Phase Transition
Spacing
spacing
Electro-optics
Raman Spectroscopy
Tilt
electro-optics
contraction
Liquid Crystal
Order Parameter
Raman spectroscopy
Contraction
liquid crystals
Liquid
First-order
expansion
Imply
Angle

Keywords

  • ferroelectric liquid-crystals
  • x-ray scattering
  • spontaneous polarization
  • order parameters
  • transitions
  • expansion
  • cells

Cite this

Chang, H. S., Jaradat, S., Gleeson, H. F., Dierking, I., Osipov, M. A., & Samsung Electronics Co. (Funder) (2009). Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants. Physical Review E, 79(6). https://doi.org/10.1103/PhysRevE.79.061706
Chang, H.S. ; Jaradat, S. ; Gleeson, H.F. ; Dierking, I. ; Osipov, M.A. ; Samsung Electronics Co. (Funder). / Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants. In: Physical Review E. 2009 ; Vol. 79, No. 6.
@article{0ce7afde2f794890a8c828cf0626a07a,
title = "Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants",
abstract = "A series of mixtures comprising an antiferroelectric liquid-crystal host and a chiral dopant is described in which the layer spacing variation at the orthogonal smectic-A* (SmA*) to tilted smectic-C* or smectic-C-alpha* (SmC* or SmC alpha*) phase transition changes from the usual strong contraction in the pure system to one in which there is almost no layer spacing change observed across the transition for dopant concentrations of 7{\%}. The nature of the orthogonal to tilted phase transition is examined using Raman spectroscopy, to determine the order parameters < P-2 > and < P-4 > in the SmA* phase, and via a generalized Landau expansion to reveal the details of the phase transition itself. The results show that the value of < P-2 > at the orthogonal to tilted transition increases from around 0.6 to 0.7 as the dopant concentration increases, while < P-4 > remains constant at approximately 0.4 irrespective of dopant concentration. Further, the generalized Landau potential measurements prove that the transition is purely second order, while electro-optic measurements confirm that the tilt angle at the transition becomes smaller with increasing dopant concentration. The combined data show that the high-temperature tilted phase regime corresponds to a SmC alpha* phase rather than the mechanism suggested by de Vries that is inferred by the layer spacing data alone. We demonstrate that the lower-temperature SmC alpha*-SmC* phase transition is of first order. Further, the temperature range of the SmC alpha* phase increases dramatically with concentration, from around 2 K in the pure system to around 21 K in the 8{\%} doped mixture, showing that the chiral dopant plays a role in stabilizing this phase. Indeed, we particularly note that for the 8{\%} doped mixture all other SmC*-like phases disappear and that the only tilted phase remaining is SmC alpha*. This implies that we are reporting a liquid-crystalline phase sequence, namely, cryst.-SmC alpha*-SmA*-iso., i.e., a direct transition between the SmC alpha* phase and the crystalline phase.",
keywords = "ferroelectric liquid-crystals, x-ray scattering, spontaneous polarization, order parameters, transitions, expansion, cells",
author = "H.S. Chang and S. Jaradat and H.F. Gleeson and I. Dierking and M.A. Osipov and {Samsung Electronics Co. (Funder)}",
year = "2009",
month = "6",
doi = "10.1103/PhysRevE.79.061706",
language = "English",
volume = "79",
journal = "Physical Review E",
issn = "1539-3755",
publisher = "American Physical Society",
number = "6",

}

Chang, HS, Jaradat, S, Gleeson, HF, Dierking, I, Osipov, MA & Samsung Electronics Co. (Funder) 2009, 'Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants' Physical Review E, vol. 79, no. 6. https://doi.org/10.1103/PhysRevE.79.061706

Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants. / Chang, H.S.; Jaradat, S.; Gleeson, H.F.; Dierking, I.; Osipov, M.A.; Samsung Electronics Co. (Funder).

In: Physical Review E, Vol. 79, No. 6, 06.2009.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants

AU - Chang, H.S.

AU - Jaradat, S.

AU - Gleeson, H.F.

AU - Dierking, I.

AU - Osipov, M.A.

AU - Samsung Electronics Co. (Funder)

PY - 2009/6

Y1 - 2009/6

N2 - A series of mixtures comprising an antiferroelectric liquid-crystal host and a chiral dopant is described in which the layer spacing variation at the orthogonal smectic-A* (SmA*) to tilted smectic-C* or smectic-C-alpha* (SmC* or SmC alpha*) phase transition changes from the usual strong contraction in the pure system to one in which there is almost no layer spacing change observed across the transition for dopant concentrations of 7%. The nature of the orthogonal to tilted phase transition is examined using Raman spectroscopy, to determine the order parameters < P-2 > and < P-4 > in the SmA* phase, and via a generalized Landau expansion to reveal the details of the phase transition itself. The results show that the value of < P-2 > at the orthogonal to tilted transition increases from around 0.6 to 0.7 as the dopant concentration increases, while < P-4 > remains constant at approximately 0.4 irrespective of dopant concentration. Further, the generalized Landau potential measurements prove that the transition is purely second order, while electro-optic measurements confirm that the tilt angle at the transition becomes smaller with increasing dopant concentration. The combined data show that the high-temperature tilted phase regime corresponds to a SmC alpha* phase rather than the mechanism suggested by de Vries that is inferred by the layer spacing data alone. We demonstrate that the lower-temperature SmC alpha*-SmC* phase transition is of first order. Further, the temperature range of the SmC alpha* phase increases dramatically with concentration, from around 2 K in the pure system to around 21 K in the 8% doped mixture, showing that the chiral dopant plays a role in stabilizing this phase. Indeed, we particularly note that for the 8% doped mixture all other SmC*-like phases disappear and that the only tilted phase remaining is SmC alpha*. This implies that we are reporting a liquid-crystalline phase sequence, namely, cryst.-SmC alpha*-SmA*-iso., i.e., a direct transition between the SmC alpha* phase and the crystalline phase.

AB - A series of mixtures comprising an antiferroelectric liquid-crystal host and a chiral dopant is described in which the layer spacing variation at the orthogonal smectic-A* (SmA*) to tilted smectic-C* or smectic-C-alpha* (SmC* or SmC alpha*) phase transition changes from the usual strong contraction in the pure system to one in which there is almost no layer spacing change observed across the transition for dopant concentrations of 7%. The nature of the orthogonal to tilted phase transition is examined using Raman spectroscopy, to determine the order parameters < P-2 > and < P-4 > in the SmA* phase, and via a generalized Landau expansion to reveal the details of the phase transition itself. The results show that the value of < P-2 > at the orthogonal to tilted transition increases from around 0.6 to 0.7 as the dopant concentration increases, while < P-4 > remains constant at approximately 0.4 irrespective of dopant concentration. Further, the generalized Landau potential measurements prove that the transition is purely second order, while electro-optic measurements confirm that the tilt angle at the transition becomes smaller with increasing dopant concentration. The combined data show that the high-temperature tilted phase regime corresponds to a SmC alpha* phase rather than the mechanism suggested by de Vries that is inferred by the layer spacing data alone. We demonstrate that the lower-temperature SmC alpha*-SmC* phase transition is of first order. Further, the temperature range of the SmC alpha* phase increases dramatically with concentration, from around 2 K in the pure system to around 21 K in the 8% doped mixture, showing that the chiral dopant plays a role in stabilizing this phase. Indeed, we particularly note that for the 8% doped mixture all other SmC*-like phases disappear and that the only tilted phase remaining is SmC alpha*. This implies that we are reporting a liquid-crystalline phase sequence, namely, cryst.-SmC alpha*-SmA*-iso., i.e., a direct transition between the SmC alpha* phase and the crystalline phase.

KW - ferroelectric liquid-crystals

KW - x-ray scattering

KW - spontaneous polarization

KW - order parameters

KW - transitions

KW - expansion

KW - cells

UR - http://dx.doi.org/ 10.1103/PhysRevE.79.061706

U2 - 10.1103/PhysRevE.79.061706

DO - 10.1103/PhysRevE.79.061706

M3 - Article

VL - 79

JO - Physical Review E

T2 - Physical Review E

JF - Physical Review E

SN - 1539-3755

IS - 6

ER -

Chang HS, Jaradat S, Gleeson HF, Dierking I, Osipov MA, Samsung Electronics Co. (Funder). Stabilization of the smectic-c-alpha* phase in mixtures with chiral dopants. Physical Review E. 2009 Jun;79(6). https://doi.org/10.1103/PhysRevE.79.061706