Field induced transitions in smectic a phases

Abstract

2014 Des transitions de l'orientation moléculaire induites par un champ électrique ou magnétique ont été mises en évidence dans différents composes smectiques A. Deux régimes de distorsion ont été observés : 2014 près de la transition smectique A ~ nématique, une distorsion périodique, de vecteur d'onde perpendiculaire au plan (n, n0) ; 2014 à plus basse température, deux réseaux périodiques de défauts, perpendiculaires au plan (n, n0) permettent le pliage des couches. Les dépendances du champ seuil en fonction de l'épaisseur de l'échantillon et de la température, et la variation de l'angle de basculement des molécules en fonction du champ appliqué sont discutées pour le second régime de distorsion. Abstract. 2014 Observations of electric and magnetic field induced transitions of the molecular orientation in smectics A are presented. Two regimes of distortion can be distinguished : 2014 close to the nematic/smectic A transition, a periodic distortion appears with a wave vector normal to the plane (n, n0). 2014 for lower temperatures, two periodic arrays of defects, normal to the plane (n, n0), allow for the folding of the smectic layers. The dependence of threshold field versus sample thickness and temperature, and the variation of the tilt angle of the molecules versus applied field are discussed for the second regime of distortion.

Surface Anchoring and Growth Pattern of the Field-Driven First-Order Transition in a Smectic-ALiquid Crystal

“…, by a sharp interface between the domain and homeotropic phases (see [8] and discussion below). In fact, field-induced transitions have been detected in Sm-A with s, ( 0 [9]; however, the scenario of the process has not been reported. The nucleation of TDs was observed for the lyotropic Sm-A mixed with ferrofluid [10].…”

Formation of a smectic A phase from a strongly deformed planar nematic liquid crystal CBOOA

“…Goscianski et al [40] consider the possibility of grain-boundary generation resulting from competition between surface anchoring and the bulk electric deforming torques for liquid crystals 40 …”

“…Compétition between wall alignment and electric field alignment (in the nematic phase) in a SmA. -A number of wôrkers have considered possibilities for the matching of the surface orientation with the bulk orientation of the liquid crystal molecules, including grain boundaries [36], [37], [40], [67], or systems of focal conics [36], [37] filling the available space by Appolonian packing (Fig. 13).…”

Applications of Smectic and Cholesteric Liquid Crystals

“…The application of even higher voltage to a smectic A with low conductivity and £11 > £1 induces a planar to homeotropic transition induced by the dielectric torque [15,16], although some of the effects described above still occur at intermediate voltages, and if the smectic has negative dielectric anisotropy (£/1 < £1) an electric field induces a homeotropic to planar transition [16]. Both field transitions occur in 10 to 100 msec when 100 V signal is applied.…”