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Analysis of deformations of flexoelectric homeotropic liquid crystal layers with various anchoring strengths

Buczkowska M., Derfel G.

Opto-Electronics Review

2011

Vol. 19, No. 1

56-60

Deformations of homeotropic layers of nematic liquid crystal possessing flexoelectric properties and subjected to external dc voltage were studied numerically. The influence of the anchoring strengthWwas investigated. The calculations were performed for two types of layers, one with positive dielectric anisotropy and positive sum of flexoelectric coefficients and the other with opposite signs of these parameters. Strongly blocking electrodes were assumed. The threshold voltages for deformations were computed for several anchoring strength values and for low, moderate, and high ion contents. The director distributions were also determined. They were influenced by joined effects of anchoring strength and space charge of ions. For increasing ion contents and increasing anchoring strength, remarkable change of deformation character was noticed. In the case of negative dielectric and flexoelectric parameters, the threshold was nearly proportional to W for low anchoring strength and saturated at some high value of W. In the case of positive dielectric and flexoelectric parameters, the threshold voltage increased strongly with W. In the range of enhanced ion concentrations, the deformation arose in two voltage ranges. The increasing anchoring strength damped the deformations in the whole layer, however, this effect was minor at high ion content.

Numerical studies of significance of anchoring strength energy for behaviour of flexoelectric homeotropic nematic layer subjected to dc electric field

Buczkowska M., Grzelczak K.

Scientific Bulletin. Physics / Lodz University of Technology

2009

Vol. 30

5-18

Elastic deformations of homeotropic nematic liquid crystal layers subjected to a d.c. electric field were studied numerically. The flexoelectric properties of the nematic material and the presence of ionic space charge were taken into account. The influence of anchoring strength W was investigated. The calculations were performed for layers with negative dielectric anisotropy and negative sum of flexoelectric coefficients. Strongly blocking electrodes were assumed. The threshold voltages for deformations were computed for several anchoring strength values and for low, moderate and high ion content. Its value was nearly proportional to W for low anchoring strength and saturated at some high value of W. The director distributions were also determined. This task was complicated by the presence of space charge of ions. Remarkable change of deformation character was noticed when the ion content and anchoring strength were varied.

Zbadano numerycznie wpływ energii kotwiczenia ciekłego kryształu z podłożem na indukowane stałym polem elektrycznym deformacje homeotropowej warstwy nematyka o ujemnej anizotropii dielektrycznej i ujemnej sumie współczynników fleksoelektrycznych. Przy niskiej zawartości jonów i wysokiej energii kotwiczenia stwierdzono symetryczny rozkład direktora. W miarę wzrostu koncentracji jonów lub obniżania energii kotwiczenia deformacja stawała się asymetryczna. Wyniki pokazują, że jonowy ładunek przestrzenny wpływa znacząco na efektywność oddziaływań powierzchniowych.