Molecular dynamics simulation of condensed-phase chiral molecular propellers

Chemical Leslie effect in a chiral smectic-C^{★} film: Nonsingular target patterns

We analyze experimentally and theoretically the winding and unwinding of the c[over ⃗] director in a chiral smectic-C^{★} film crossed by an ethanol flow. This leads to a target pattern under crossed polarizers when the +1 defect imposed by the boundary conditions is pinned on the edge of the film. We show that the target is deformed at the center of the film when it is subjected to a flow of ethanol because of the presence of two recirculation vortices of chemohydrodynamical origin. This deformation and the two vortices disappear during the unwinding of the target when the ethanol flow is stopped. This unambiguously shows that the target deformation is due to the vortices and not to the elastic anisotropy. These two points are confirmed theoretically. An estimate of the two so-called chemomechanical and chemohydrodynamical Leslie coefficients is also derived from this study.

Chemical Leslie effect in Langmuir monolayers: a complete experimental characterization

We propose a complete characterization of the chemical Leslie effect in a Langmuir monolayer of a chiral liquid crystal. To reach this goal, we developed new experimental techniques using an electric field and a humidifier to prepare large monodomains in which the molecules can freely rotate. We also designed six independent experiments to precisely measure the four material constants involved in the dynamics of the monolayer, namely the Leslie coefficient, the rotational viscosity, the curvature elasticity constant and the surface polarization. The relevance of the inverse Leslie effect is also discussed.

Thermomechanical coupling in coarse grained cholesteric liquid crystal model systems with pitches of realistic length

Cholesteric liquid crystal where the director is rotated by a temperature gradient.

Director/barycentric rotation in cholesteric droplets under temperature gradient

When a chiral liquid crystal is given a transport current, a unidirectional molecular motion is known to take place, which is called the Lehmann effect. In this paper, we study the mysterious heat-current-driven Lehmann effect using two types of hemispherical cholesteric droplets using polarizing, reflecting, confocal and fluorescent microscopies. Both the droplets, coexisting with the isotropic phase and contacting on a glass substrate, are characterized by the concavo-convex modulated surface and the inside orientational helix. Further, the only difference between them is the helical axis direction; i.e., one is perpendicular and the other is parallel to the substrate. Under the temperature gradient perpendicular to the substrate, the droplet whose helical axis is parallel to the heat current exhibited pure director rotation, while that with the axis perpendicular to the current rotated independently as a rigid body. In the two droplets, the rotational conversion efficiency from the temperature gradient into the angular velocity showed very different dependences on the chirality strength and on the droplets' size, suggesting that the rotations of the two droplets may be driven by independent torques with different origins. This is the first observation that the cholesteric droplets under the temperature gradient exhibit the two rotational modes, the pure director rotation and the molecular barycentric motion, which can be switched to each other by changing the heat-current direction parallel and perpendicular to the helical axis.