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Influence of tilted surface alignment on flexoelectric domains in twisted nematic layers

Buczkowska M., Derfel G.

Scientific Bulletin. Physics / Lodz University of Technology

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2017

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Vol. 38

5--10

EN

The small deformations induced by electric field in twisted flexoelectric nematic layers were simulated numerically. The onedimensional (i.e. homogeneous over the whole area of the layer) and two-dimensional (i.e. spatially periodic flexoelectric domains) deformations were considered. It was shown that the periodic deformations do not arise if sufficiently high pretilt angle is imposed by the boundary conditions. The value of pretilt angle necessary for elimination of domains increases with the flexoelectric coefficient e33. This result is of practical meaning because the flexoelectric domains are undesirable from an applicative point of view since they destroy the homogeneous appearance of the area of an excited pixel of a display.

PL

Niewielkie odkształcenia wywołane polem elektrycznym w warstwach skręconego nematyka były symulowane numerycznie. Badano odkształcenia jednowymiarowe (tj. jednorodne na całej powierzchni warstwy) i dwuwymiarowe (tj. przestrzennie okresowe). Wykazano, że odkształcenia okresowe nie powstają, gdy warunki brzegowe narzucają odpowiednio duży kąt nachylenia uporządkowania powierzchniowego. Jego wartość rośnie ze wzrostem współczynnika fleksoelektrycznego e33. Wynik ten ma znaczenie praktyczne, ponieważ występowanie domen fleksoelektrycznych w urządzeniach ciekłokrystalicznych jest niepożądane.

2

Threshold voltages and optical retardation of deformed flexoelectric nematic layers with asymmetric surface anchoring

Derfel G., Buczkowska M.

Opto-Electronics Review

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2013

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Vol. 21, No. 2

205-209

EN

Deformations of homeotropically aligned flexoelectric nematic layers induced by dc electric fields were simulated numerically. Two different anchoring strengths on the limiting surfaces were assumed. Nematic material was characterised by negative dielectric anisotropy. Both signs of the sum of flexoelectric coefficients were taken into account. The electric properties of the layer were described in terms of a weak electrolyte model. Mobility of cations was assumed to be one order of magnitude lower than that of anions. Quasi-blocking electrode contacts were assumed. The threshold voltages for deformations were determined by means of calculations of the phase difference Φ between ordinary and extraordinary light rays passing through a layer placed between crossed polarisers. The threshold values depended on the polarity of the bias voltage U. When the threshold value was exceeded, the phase difference increased with the voltage. Two different Φ(U/Uthreshold) dependencies for the two polarities of the voltage were found for each layer if the nematic possessed the flexoelectric properties. The possibility of using this effect to detect the flexoelectricity in the nematic was explored by simulated experiments. The effectiveness of the proposed method is discussed.

3

Temporal characteristics of dc electric field induced deformations of flexoelectric nematic layers

Derfel G., Buczkowska M.

Scientific Bulletin. Physics / Lodz University of Technology

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2012

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Vol. 33

31-37

EN

Dynamics of DC electric field induced deformations of flexoelectric nematic layers were studied numerically. The characteristic response times were calculated. It was found that the cooperative effect of flexoelectricity and of ionic space charge may affect the dynamics of the deformations even in the case of rigid anchoring.

PL

Zbadano numerycznie dynamikę odkształceń wywołanych stałym polem elektrycznym w warstwach nematyków posiadających właściwości fleksoelektryczne. Obliczono charakterystyczne czasy odpowiedzi w funkcji sumy współczynników fleksoelektrycznych. Wyniki pokazują, że jednoczesne działanie momentów fleksoelektrycznych i jonowego ładunku przestrzennego wpływa na dynamikę odkształceń nawet w warunkach sztywnej orientacji powierzchniowej.