Three-dimensional imaging of dielectric patterns in electrohydrodynamic convection of a nematic liquid crystal

Abstract

The transition from surface to bulk normal dielectric rolls in a nematic liquid crystal is imaged by fluorescence confocal polarizing microscopy. The three-dimensional director structure and the liquid flow are scanned in both the layer plane and the transverse plane. Two systems of small-scale convective flow are formed, one at each electrode. Strong anchoring makes director oscillations difficult and charges accumulate by the Carr-Helfrich mechanism. The middle region is a structureless convection where the director oscillates with the frequency of the applied voltage. The small-scale flow eventually fills the cell from one electrode to the other as one system of thin and elongated rolls. The true dielectric mode is not a director pattern, rather a surface flow instability.

Inhibited pattern formation by asymmetrical high-voltage excitation in nematic fluids

“…Some earlier reports indicated that the dielectric EC rolls are rather localized at the cell surfaces than in the bulk [29,30]. Taking into account that significant electric field gradients may exist on the length scale of the dielectric rolls in the vicinity of the electrodes, this might account for why the behavior of dielectric EC is more anomalous than the conductive EC.…”

“…We anticipate that ionic effects originating in the electrolytic nature of liquid crystals, such as voltage dependent conductivity (electro-purification), internal voltage attenuation in the cell, and Debye layers at the boundaries may play an important role. Some earlier reports indicated that the dielectric EC rolls are rather localized at the cell surfaces than in the bulk [29,30]. Taking into account that significant electric field gradients may exist on the length scale of the dielectric rolls in the vicinity of the electrodes, this might account for why the behavior of dielectric EC is more anomalous than the conductive EC.…”

Single Molecule Spectroscopy of Conjugated Polymer Chains in an Electric Field-Aligned Liquid Crystal

“…The effect of an applied E-field on the local order of LC solvents is of interest in fundamental science and flat-panel display applications. The director orientation at the device interface has been measured by many techniques including optical − and acoustic − methods and has been explained by a elastic continuum theory. , …”

LCP droplet dispersions: a two-phase, diffuse-interface kinetic theory and global droplet defect predictions

“…There are myriad applications, from optical to acoustic wave propagation, which lead one to explore the limits of LC and LCP droplet size and droplet arrays that can be achieved by controlled flow conditions. We refer the reader to the review 6 for optical applications of polymer-dispersed liquid crystals and to papers by Smalyukh and colleagues [7][8][9][10][11] for additional applications.…”