Azimuthal director gliding at a strongly anchoring interface of polyimide

Abstract

A gliding of the director at the interface between a nematic liquid crystal and a solid medium is generally observed at many interfaces giving weak or moderately strong anchoring. This phenomenon is characterized by strongly non-linear dynamics and very long relaxation times (hours-days). The gliding of the director has also been observed very recently at the interface between a rubbed polyimide layer and a nematic liquid crystal which gives strong azimuthal anchoring. However, due to the weak nature of the experimental signals that characterizes the strong anchoring, this latter measurement was appreciably affected by thermal drift. In this paper, we develop a new experimental reflectometric method whereby the thermal drift is appreciably reduced. The method allows us to obtain more accurate signals and to investigate their time dependence. It is shown that the director gliding is well represented by a stretched exponential, as well as in the case of weak anchoring substrates. These measurements confirm that the gliding of the director is a universal phenomenon characterizing any kind of substrate with either weak and strong anchoring

Photoinduced gliding of the surface director in azo‐dye doped nematic liquid crystals

“…Figures 3 and 4 are most typical with a50.44 when chisquared is minimized. This is similar to the findings of Faetti et al [1] for gliding from an external electric field and Faetti and Marianelli's [9] determination of a50.362. In comparing different sets of data, we used a value of a50.44, even when that value did not minimize chi-squared, because time constants can vary slightly with this exponent and changes in chi-squared were not significant.…”

“…The slow regime, on the other hand, shows the surface director angle changing continuously without appearing to reach a stationary value. Most studies indicate that the slow dynamics associated with gliding can be characterized either by a stretched exponential [1,9] or a power law [5]. Another characteristic of gliding is that it is not only slow, but appears to be plastic; there is a memory effect [10].…”

Electrically assisted light-induced azimuthal gliding of the nematic liquid-crystal easy axis on photoaligned substrates

“…It turned out that the easy axis itself may slowly rotate under the action of strong (magnetic or electric) fields. Over the past few decades this slow motion -the socalled easy axis gliding -has received much attention * Email address: kiselev@iop.kiev.ua † Email address: eechigr@ust.hk as a widespread phenomenon observed in a variety of liquid crystals on amorphous glass [3], polymer [4][5][6][7][8][9][10][11][12][13] and solid [6,11] substrates. Recently, it was found that, in addition to magnetically (electrically) induced gliding, there is the photoinduced gliding of the easy axis in dye-doped liquid crystals [14,15].…”

Director gliding in a nematic liquid crystal layer: Quantitative comparison with experiments

“…Zenithal director gliding is observed as an electric field is applied perpendicular to the bounding plates [6] and after the applied electric field is removed [6,10]. By contrast, azimuthal gliding is observed as an electric field is applied parallel to the plates [12].…”

“…In the case of zenithal gliding we consider two sets of experiments, carried out by Joly et al [6] and Buluy et al [10], that focus on zenithal gliding in the presence of an electric field and after the electric field is turned off. In the case of azimuthal gliding, we consider the experiment carried out by Faetti & Marianelli [12], which provides evidence for azimuthal director gliding of a strongly anchored system as an electric field is applied across the layer. Zenithal director gliding is observed as an electric field is applied perpendicular to the bounding plates [6] and after the applied electric field is removed [6,10].…”