Electro-optic and dielectric study of the de Vries–type smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mi>A</mml:mi><mml:mo>∗</mml:mo></mml:msup></mml:mrow></mml:math>phase exhibiting transitions to smectic-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mi>C</mml:mi><mml:mi>A</mml:mi><mml:mo>∗</mml:mo></mml:msubsup></mml:mrow></mml:math>and smectic-<mml:math xmlns:mml="http://www.w3.org/1998/M

Manna, Uttam; Song, Jang‐Kun; Panarin, Yu. P.; Fukuda, Atsuo; Vij, J. K.

doi:10.1103/physreve.77.041707

Cited by 34 publications

(35 citation statements)

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“…As a result, the birefringence increases significantly upon transition from de Vries-type SmA ‫ء‬ phase to SmC ‫ء‬ phase. 15,18 For TSiKN65, we find that the birefringence goes up by around 43% upon transition from SmA ‫ء‬ to SmC ‫ء‬ phase, as shown in Fig. 1͑d͒.…”

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Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

Manna

Song

Vij

et al. 2009

Applied Physics Letters

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We investigate the response time of an electroclinic liquid crystal with large induced tilt and polarization ͑de Vries smectic A ‫ء‬ ͒. The response time is found to increase with the increase in electric field up to a threshold value in contrast with the general case of a decrease with field. This behavior is unusual and contrasts with that observed for a conventional smectic-A ‫ء‬ phase. The anomalous behavior is explained by the Langevin process of the director reorientation by assuming an increase in the effective dipole moment ͑ eff ͒ with field. The response time decreases with the increase in temperature in the smectic-A ‫ء‬ phase. We find the existence of a finite correlation length of a few tens of nm which in both temperature and field dependent. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3049319͔ An electric field E applied parallel to the layer of a chiral smectic-A ‫ء‬ ͑SmA ‫ء‬ ͒ phase induces a molecular tilt relative to the layer normal in a plane orthogonal to the field, which is called the electroclinic effect. 1 This can be described by a phenomenological model that predicts a linear dependence of the induced tilt angle on the applied field E for low field strengths. This is given bywhere c is the electroclinic coupling constant, ␣ 0 is a phenomenological constant, and T AC is SmA ‫ء‬ -SmC ‫ء‬ transition temperature. The electroclinic effect is a unique and technologically useful electro-optical property of a chiral SmA ‫ء‬ liquid crystal. Electroclinic liquid crystals have a potential for development of projection displays, spatial light modulators, optical correlators, smart pixel image processors, etc., where speed, high contrast, and gray scale are of the utmost importance.2-4 However, application of electric field in the SmA ‫ء‬ phase parallel to the smectic layers induces stripes arising from a reduction in the layer spacing due to the molecular tilting and a consequent smectic layer buckling. 5,6 This has a detrimental effect on the contrast ratio of electrooptic devices. 7,8 As a result, the SmA ‫ء‬ materials having zero or low layer shrinkage with decreasing temperature or increasing field have drawn significant scientific interest due to their potential for applications in display and photonic devices. 9 In the de Vries' "diffuse cone model" of these materials, the molecular long axis, and presumably the local director, is tilted by a finite angle. However, it is azimuthally randomized with uniform distribution f͑͒ =1/ 2 on a cone from layer to layer as well as within a single layer, 10-12 while the macroscopic director lies along the layer normal. Application of electric field tends to align the transverse dipoles, and this gives rise to a large electroclinic effect, the induced tilt, and the polarization. [13][14][15] In this letter, we report an anomalous behavior of the response time in an electroclinic liquid crystal having small layer contraction, large induced tilt, and polarization. We find that the response time increases in the de Vries-type SmA ‫ء‬ phase up to a ...

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Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

Manna

Song

Vij

et al. 2009

Applied Physics Letters

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“…Our model also predicts (for materials with excluded volume inter actions) the possibility of birefringence that decreases as the AC tran sition is approached from the A phase, which as discussed above, is an unusual feature that has been observed experimentally [8,9]. For any of the three types of transitions D Dn decreases linearly with tempera ture as the transition is approached from the A phase, as shown in Figure 7.…”

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“…This is consistent with the general observation [7] that de Vries materials have unusually strong layering order and unusually weak orienta tional order. Additionally, only by including temperature dependent layering, does one predict [10] the unusual, yet experimentally observed [8,9], possibility of a nonmonotonic temperature dependence of birefringence.…”

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“…Some de Vries materials exhibit another unusual feature, namely a birefringence that varies nonmonotonically with temperature [8,9]; in particular, the birefringence decreases as the AC transition is approached from within the A phase. De Vries materials generally seem to have unusually small orientational order and follow the phase sequence isotropic (I) � A � C. In several de Vries materials, the AC transition seems to occur close to tricriticality [12,13].…”

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de Vries Behavior in Smectics near a Biaxiality Induced Smectic A – Smectic C Tricritical Point

Saunders

2009

Molecular Crystals and Liquid Crystals

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We show that a generalized Landau theory for the smectic A and C phases exhibits a biaxiality induced AC tricritical point. Proximity to this tricritical point depends on the degree of orientational order in the system; for sufficiently large orientational order the AC transition is 3D XY like, while for sufficiently small orientational order, it is either tricritical or 1st order. We investigate each of the three types of AC transitions near tricriticality and show that for each type of transition, small orientational order implies de Vries behavior in the layer spacing, an unusually small layer contraction. This result is consistent with, and can be understood in terms of, the ''diffuse cone'' model of de Vries. Additionally, we show that birefrin gence grows upon entry to the C phase. For a continuous transition, this growth is more rapid the closer the transition is to tricriticality. Our model also predicts the possibility of a nonmontonic temperature dependence of birefringence.

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“…The increase in birefringence is associated with an increase in orientational order. Some de Vries materials exhibit another unusual feature, namely a birefringence that varies nonmonotonically with temperature [2,3]. Specifically, the birefringence decreases as the Sm-A * -Sm-C * transition is approached from either the low or the high temperature side.…”

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de Vries behavior of the electroclinic effect in the smectic-A∗phase near a biaxiality-induced smectic-A∗–smectic-<

Saunders

2009

Phys. Rev. E

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Using a generalized Landau theory involving orientational, layering, tilt, and biaxial order parameters we analyze the smectic-A * and smectic-C * (Sm-A * -Sm-C * ) transition, showing that a combination of small orientational order and large layering order leads to Sm-A * -Sm-C * transitions that are either continuous and close to tricriticality or first order. The model predicts that in such systems the increase in birefringence upon entry to the Sm-C * phase will be especially rapid. It also predicts that the change in layer spacing at the Sm-A * -Sm-C * transition will be proportional to the orientational order. These are two hallmarks of Sm-A * -Sm-C * transitions in de Vries materials. We analyze the electroclinic effect in the Sm-A * phase and show that as a result of the zero-field Sm-A * -Sm-C * transition being either continuous and close to tricriticality or first order (i.e for systems with a combination of weak orientational order and strong layering order) the electroclinic response of the tilt will be unusually strong. Additionally, we investigate the associated electrically induced change in birefringence and layer spacing, demonstrating de Vries behavior for each, i.e. an unusually large increase in birefringence and an unusually small layer contraction. Both the induced change in birefringence and layer spacing are shown to scale quadratically with the induced tilt angle.

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Electro-optic and dielectric study of the de Vries–type smectic-A∗phase exhibiting transitions to smectic-CA∗and smectic-
Uttam Manna
¹
,
Jang‐Kun Song
²
,
Yu. P. Panarin
³

et al.

Cited by 34 publications

References 47 publications

Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

de Vries Behavior in Smectics near a Biaxiality Induced Smectic A – Smectic C Tricritical Point

de Vries behavior of the electroclinic effect in the smectic-A∗phase near a biaxiality-induced smectic-A∗–smectic-<

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Electro-optic and dielectric study of the de Vries–type smectic-A∗phase exhibiting transitions to smectic-CA∗and smectic-Uttam Manna1, Jang‐Kun Song2, Yu. P. Panarin3 et al.

Cited by 34 publications

References 47 publications

Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

Anomalous dependence of response time on the electric field in an electroclinic liquid crystal with large induced tilt and polarization

de Vries Behavior in Smectics near a Biaxiality Induced Smectic A – Smectic C Tricritical Point

de Vries behavior of the electroclinic effect in the smectic-A∗phase near a biaxiality-induced smectic-A∗–smectic-<

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About

Electro-optic and dielectric study of the de Vries–type smectic-A∗phase exhibiting transitions to smectic-CA∗and smectic-
Uttam Manna
¹
,
Jang‐Kun Song
²
,
Yu. P. Panarin
³

et al.