Molecular simulation of chevrons in confined smectic liquid crystals

Abstract

Chevron structures adopted by confined smectic liquid crystals are investigated via molecular dynamics simulations of the Gay-Berne model. The chevrons are formed by quenching nematic films confined between aligning planar substrates whose easy axes have opposing azimuthal components. When the substrates are perfectly smooth, the chevron formed migrates rapidly towards one of the confining walls to yield a tilted layer structure. However, when substrate roughness is included, by introducing a small-amplitude modulation to the particlesubstrate interaction well-depth, a symmetric chevron is formed which remains stable over sufficiently long runtimes for detailed structural information, such as the relevant order parameters and director orientation, to be determined. For both smooth and rough boundaries, the smectic order parameter remains non-zero across the entire chevron, implying that layer identity is maintained across the chevron tip. Also, when the surface-stabilised chevron does eventually revert to a tilted layer structure, it does so via surface slippage, such that layer integrity is maintained throughout the chevron to tilted layer relaxation process.

Determination of optimal chevron configurations in surface-stabilized smectic C*

“…Это связано с тем, что длина смектического слоя при заданной температуре, вследствие постоянно-го наклона [величина угла зависит θ от температуры] директора в слое SmC* остаётся постоянной. Ассиме-тричные шевронные структуры были ранее рассмотре-ны в работах [7,8]. Выбор такой модели связан также и с тем обстоятельством, что мы рассматриваем молеку-лярный слой SmC* с жестким сцеплением с подложками вне массопереноса вещества при изменении конфигу-рации шеврона.…”

“…Подставив решение уравнения (6) -функцию φ(x) в функционал f, получим выражение для энергии смек-тического слоя, приходящуюся на единицу площади (8) где d = 5 мкм. Сопоставив значения F при ξ = {−0.2d; −0.1d; 0}, можно заключить, что свободная энергия минимальна, если слой SmC* сломан в центре между подложками.…”

On the biaxiality of smectic C and ferroelectric liquid crystals

“…Instead, simpler approaches have been taken, such as the empirical approach used in reference [24], or the Landau de Gennes [25] or numerical modelling [26] approaches. In the former approach, the transition is effectively instantaneous and discontinuous when the gradients of the cdirector reach a critical torque T 0 .…”

Using particle shape to induce tilted and bistable liquid crystal anchoring

“…[30][31][32][33], this contact function was used as the basis for the particle-substrate interaction: the surface, as viewed by any particle, was taken to be represented by a sphere located in the surface plane but with the same x-and y-coordinates as those of the particle. In this Section, we adopt this same HGO-sphere approximation for the particle-substrate contact function.…”

“…Homeotropic anchoring has been achieved using hard-particle systems employing non-additive wall-particle interactions at perfectly flat walls [11,19,20,24,25] and full interactions at walls with tethered flexible chains [25][26][27] and rigid rods [28]. While homeotropic anchoring has been seen in simulations of Gay-Berne particles confined by smooth substrates [21], and could certainly be forced using the well-depth anisotropy tuning approach employed in [29], the majority of such systems have yielded tilted alignments [30][31][32][33]. Up to now, the tilt observed in these systems has been ascribed to competition between the particle-particle and particle-wall attractive interactions.…”