Dynamics of s =1/2 disclinations in twisted nematics

Abstract

RCsumi.-Les auteurs ktudient du point de vue thkorique et expkrimental les lignes de disinclinaisons qui skparent des rkgions d'orientation opposee dans la structure twistke d'un cristal liquide nkmatique. 11s consacrent une attention particulikre aux mouvements des lignes de disinclinaison induits par un champ magnktique. La comparaison des rksultats thkoriques et experimentaux aboutit a une estimation des dimensions du cceur de la disinclinaison. On obtient accessoirement I'knergie klastique d'une ligne de disinclinaison. 11s donnent un modtle physique simple de l'effet combink des forces magnetiques, induites par courbure et dissipatives qui agissent sur une ligne de disinclinaison.

Effect of director distortions on morphologies of phase separation in liquid crystals

“…The rubbing directions at the two plates of the cell are perpendicular to each other. The equally probable domains of opposite 90 • twists, (n x , n y , n z ) = (cos πz/2d, sin πz/2d, 0) and (n x , n y , n z ) = (cos πz/2d, − sin πz/2d, 0) (the z axis is perpendicular to the cell plates), are separated by defects (disclinations [20]). The cell configuration allows us to separate the lens and light polarization effects from the effect of director distortions, by chosing P||n at the plate of incidence, Fig.2,3.…”

The influence of homeotropic and planar boundary conditions on the field induced cholesteric-nematic transition

“…Before continuing with equation (4), we now first determine q as function of qo and d. Therefore we calculate the elastic free energy density averaged over the thickness d and the period p = 2 n/q. Since dk dz = dx dT(T2 + T2 )-' and dx = -du/2 u we find in a first approximation The upperbound uo stems from the fact that we have to exclude the singular region at k = 0, z = 0, where the orientation of the director is undetermined [6]. This region, known as a disclination, can be assumed to have a cylindrical shape with a core radius a of a few molecular lengths.…”

“…This problem for 9 can be solved analytically in the domain 0 k yd/2, -7r/2 q z + 7r/2 q (since T(z) = T(-z) it is sufficient to consider 0 z n/2 q) using the technique of conformal mapping. The procedure is essentially the same as that described in references [5] and [6] and will therefore be discussed only in brief. The point is that cp(k, z) can be considered as the imaginary part of a complex function w(s) = x + icp, which is holomorphic when considered as a function of the complex variable s = k + iz in the strip 0 Im s 7T/2 q.…”

Non‐Chiral Smectic Liquid Crystals: Nonchiral Smectic Liquid Crystals — Applications

“…(2)] by Geurst and Goosens [67] who extended the Carr-Helfrich model [64] for dynamic scattering in nematics. However, these expressions consider only the torques acting on the molecules and not the ability of the dopant to disrupt the smectic layers; there are also some anomalies in the experimental work defining what is meant by the 'threshold voltage'.…”