Orientational transition in nematic liquid crystals under oscillatory Poiseuille flow

Abstract

We investigate the orientational behaviour of a homeotropically aligned nematic liquid crystal subjected to an oscillatory plane Poiseuille flow produced by an alternating pressure gradient. For small pressure amplitudes the director oscillates within the flow plane around the initial homeotropic position, whereas for higher amplitudes a spatially homogeneous transition to out-of-plane director motion was observed for the first time. The orientational transition was found to be supercritical and the measured frequency dependence of the critical pressure amplitude in the range between 2 and 20 Hz was in quantitative agreement with a recent theory.

Rheology of distorted nematic liquid crystals

“…As a result of extensive theoretical, numerical and experimental investigations, the behaviour of nematic liquid crystals in shear and Poiseuille flow fields is well documented [7][8][9][10][11][12][13]. However, as far as we are aware, results are limited to the cases where at all the boundaries of the containing cell the alignment of the director field is either free, homogeneous (parallel to the surface) or homeotropic (perpendicular to the surface).…”

“…Moreover, in twisted nematic devices the phenomenon of optical bounce, a transient rotation of the director field in the center of the cell in the wrong direction upon switching, has been well studied and is understood to be due solely to back-flow [5]. More recently, there have been detailed measurements of back-flow effects on another commonly used cell, namely the hybrid aligned nematic (HAN) cell [6].As a result of extensive theoretical, numerical and experimental investigations, the behaviour of nematic liquid crystals in shear and Poiseuille flow fields is well documented [7][8][9][10][11][12][13]. However, as far as we are aware, results are limited to the cases where at all the boundaries of the containing cell the alignment of the director field is either free, homogeneous (parallel to the surface) or homeotropic (perpendicular to the surface).…”

Flows of Anisotropic Liquids

“…It is connected with the nature of a basic state that is presented by the linear regime of an oscillating motion in the flow plane (see Section 3.3.2). [71]. The theoretical prediction of such instability was made by Krekhov and Kramer [40].…”

“…Such structure was induced by oscillating flows [40,70,71]. Such structure was induced by oscillating flows [40,70,71].…”

Analytical Solution for Thermal Convection in a Layer of Liquid Crystal With Free Surface

“…Unfortunately there are still at least two different sets of parameters for MBBA in literature (see Table I). The first column of the Table I corresponds to the data from [5,[13][14][15] (we denote it as MBBA (1)), the second one presents the data of [16][17][18][19] (called MBBA(2)). One can see that although in average those sets are rather close to each other, there are significant differences in values of such parameters as K 1 ; K 2 ; K 3 ; a 1 ; a 5 .…”