I. Dozov

Planar degenerated anchoring of liquid crystals obtained by surface memory passivation

Weak anchoring of liquid crystals on solid substrates is usually dominated by the surface memory. We show that the memory can be removed by surface passivation by silane molecules. We realize planar, azimuthally degenerated, and memory-free anchorings without pretilt.

Strong orientational coupling in two-component suspensions of rod-like nanoparticles

We consider two-component suspensions of non-magnetic and magnetic rods and show that alignment of the magnetic component by a magnetic field orients the non-magnetic one. We studied suspensions of non-magnetic V2O5 rods doped with magnetic Fe3O4 nanoparticles. In the isotropic phase, the field-induced orientation of Fe3O4 particle chains aligns the V2O5 rods. Moreover, the nematic phase reorients towards the field at ≈50 Oe, much less than the ≈5 kOe needed for pure V2O5 suspensions. Such effects should exist in any suspension of two kinds of rods, one of which is sensitive to an external field.

Fast bistable nematic display from coupled surface anchoring breaking

We present new experimental results on bistable nematic display, controlled from surface anchoring breaking. Using simple planar anchorings on both plates and chiralized 5CB material, we prepare thin cells with two equal energy states: one uniform planar and the other one twisted by 180 degrees. Applying short electric pulses we break transiently both surface anchorings (to write) or only one of them (to erase). After these short pulses, in absence of any field, we obtain at will the uniform state or the twisted one, with infinite lifetime and full bistability. Using polarizers an optical contrast of 50 is measured between the two states. The write/erase pulse duration is short, comparable with the surface anchoring response time approximately 10 microseconds. The optical response time, classically related to the cell thickness, is here in the ms range. The temperature dependence of the threshold is also discussed. The existence of the two relatively close writing and erasing thresholds allows in principle simple multiplexability.

On the sign of flexoelectric coefficients in nematic liouid crystals

Abstract We measure the distortion of a nematic liquid crystal placed in a quadrupolar field distribution. This allows the measurement of (e1+e3)/K, where e1 and e3 are the flexoelectric coefficients and K a bend curvature elastic constant. For MBBA, e1+e3 is found negative, contrary to previous estimates. For 80CB, e1+e3 is found positive. This confirms the conformational origin of flexoelectricity in this later compound.

Nematic Bistable Device Using a Metastable Anti-Conical Surface Anchoring

We propose a bistable nematic device implementing the recently observed anti-conical degenerated anchoring on a grafted polystyrene surface. The anti-conical surface presents two energy minima, planar degenerated and homeotropic, separated by a conical energy barrier. Under moderate electric field the anchoring is broken, the surface director jumps across the energy barrier and the device switches between two optically distinct bistable textures.

Development of low anchoring strength liquid crystal mixtures for bistable nematic displays

The recent Bistable Nematic (BiNem(R)) LCD technology presents long term bistability, high level passive matrix multiplexing and high optical quality. The BiNem device, based on anchoring breaking, needs specific low anchoring strength materials - alignment layers and liquid crystal mixtures. We present here our approach to develop nematic mixtures with wide enough temperature range and low zenithal anchoring energy.

Strength of Memory-Induced Anchoring of 5CB on Bare Untreated ITO

Abstract We realize uniform planar alignment of 5CB on isotropic untreated ITO substrate. The counterplate orientation is “imprinted” on ITO and memorized by adsorption of an oriented nematic layer. We measure the azimuthal and the zenithal anchoring energies. We show that the memory induced anchoring strength is similar to the one usually found for substrates with high anisotropy. Studying rubbed ITO substrate, we show that in this case also the azimuthal anchoring is mainly due to memory effect.