Electrically driven torsional distortions in twisted nematic films.

The purpose of this article is to describe the physical mechanism responsible for the appearance of both traveling and nontraveling distortions in a microsized homogeneously aligned nematic (HAN) film under the effect of a large electric field. Numerical studies have been carried out to describe both the traveling and nontraveling dynamic reorientation of the director's field in a thin, in a few tens of micrometers, the HAN film under the effect of a large electric field E (∼1.0V/µm). It is shown that in response to the electric field E applied parallel to the bounding surfaces, the torques acting on the director n[over ̂] may excite the traveling distortion wave propagating normally to both boundaries, whose resemblance to a kinklike wave increases with increasing applied electric field E. Calculations show that in the HAN film the physical mechanism that is responsible for the electric-field-induced distortion of the director field n[over ̂] in the form of traveling wave provides a much faster relaxation regime than in the case of the nontraveling mode.

Microfluidics of liquid crystals induced by laser radiation.

Several scenarios for the formation of hydrodynamic flows in microsized hybrid aligned nematic (HAN) channels, based on the appropriate nonlinear extension of the classical Ericksen-Leslie theory, supplemented by thermomechanical correction of the shear stress and Rayleigh dissipation function, as well as taking into account the entropy balance equation, are analyzed. Detailed numerical simulations were performed to elucidate the role of the heat flux q caused by laser radiation focused on the lower boundary of the equally warmed up the HAN channel containing a monolayer of azobenzene with the possibility of a trans-cis and cis-trans conformational changes in formation of the vortex flow v. It is shown that a thermally excited vortex flow is maintained with motion in a positive sense (clockwise) in the vicinity of the orientation defect at the lower boundary of the HAN channel caused by the trans-cis and cis-trans conformational changes. In the case of the same HAN channel, but without the azobenzene monolayer at the lower boundary, the heat flux q can also produce the vortical flow in the vicinity of the laser spot at the lower boundary, directed in a negative sense (counterclockwise). At that, the second vortex is characterized by a much slower speed than the vortical flow in the first case.

Nonmechanical principle for producing a flow in a homogeneously aligned microfluidic nematic channel.

Nonmechanical fluid pumping principle has been developed utilizing the interactions of both the director [Formula: see text] and velocity v fields and temperature T redistribution across a two-dimensional homogeneously-aligned nematic (HAN) microfluidic channel under the influence both of a heat flux [Formula: see text] and the surface electric field E0, originating from the surface charge density [Formula: see text]. The heat flux [Formula: see text] is caused by the laser beam pulse focused on the channel's boundary, whereas the normally directed electric field is due to electric double layers, that is naturally created within the liquid crystal near a charged surface. Calculations, based upon the nonlinear extension of the classical Ericksen-Leslie theory, with accounting the entropy balance equation, show that due to the coupling between the [Formula: see text] and [Formula: see text], in the HAN microfluidic channel the vortical flow [Formula: see text] may be excited. The direction and magnitude of [Formula: see text] is influenced by [Formula: see text] and E0, as well as by the thickness of the HAN microfluidic channel.