Electroconvection of pure nematic liquid crystals without free charge carriers

Abstract

We consider electroconvection as a response of nematic liquid crystals to an external electric AC field, in the absence of free charge carriers. Previous experimental and theoretical results emphasized charge carriers as a necessary precondition of electroconvection because free-charges in the fluid can respond to an external electric field. Therefore, ionized molecules are considered as responsible for the driving of electroconvective flows. In experiments, finite conductivity is achieved by adding charge-carrying dye molecules or in non-dyed liquid crystals by impurities of the samples. The phenomenon of electroconvection is explained by the Carr-Helfrich theory, supported by numerical simulations. In the present paper, we show that electroconvection may occur also in pure nematic liquid crystals. By means of particle-based numerical simulations we found that bound charges emerge by alignment of polarized liquid crystal molecules in response to the external electric field. In our simulations we could reproduce the characteristic features of electroconvection, such as director-flow patterns, the phase-transition in the voltage-frequency diagram, and dislocation climb/glide motion, which are well known from experiments and hydrodynamic simulations under the assumption of free charge carriers.

Origin of optical nonlinearity of photo-responsive liquid crystals revealed by transient grating imaging

“…For the simulation of the photo-induced change of LC, we performed a mesoscopic simulation based on the algorithm of liquid crystal stochastic rotational dynamics (LC-SRD) 25 . This approach uses a particle-based method and was first implemented by using the Ericksen-Leslie model for the evolution of LC bulk flows.…”

Mesoscopic simulations of active nematics

“…Alternative hybrid finite difference/MPCD approaches have been proposed to simulate nematic liquid crystals (50,51). Nematic MPCD has been used to study nematohydrodynamic fluctuations and correlations (52,53), electroconvection (54), defects around nanocolloids (49,55), and living liquid crystals (56). We now extend the nematic Andersen-thermostatted collision operator to simulate wet active nematics.…”

Mesoscopic Simulations of Active-Nematics

“…Alternative hybrid finite difference/MPCD approaches have been proposed to apply MPCD to nematic liquid crystals [67,68]. Nematic MPCD has been employed to study nematohydrodynamic fluctuations and correlations [69,70], electroconvection [71], defects around nanocolloids [66,72,73] and living liquid crystals [74]. We now extend the nematic Andersen-thermostatted collision operator to simulate wet active nematics.…”