RESUMEN
In a recent letter (P. Oswald et al., EPL 103, 46004 (2013)), we have shown that a smectic-A phase hardens in compression normal to the layers when the liquid crystal is doped with gold nanoparticles. This is due to the formation of Cottrell clouds nearby the core of the edge dislocations and the appearance of an additional drag force that reduces their mobility. We theoretically calculate the shape of the Cottrell cloud and the associated drag force as a function of the climb velocity of the dislocations. The main result is that the drag force depends on velocity and vanishes when the temperature tends to the smectic-A-to-nematic transition temperature. The role of the diffusion anisotropy is also evaluated.
RESUMEN
We show how the inclusions of the nanoparticles or the clusters of nanoparticles in the liquid-crystalline smectic-A phase lead to layer deformations and may create a tilt in their vicinity, thus inducing locally a smectic-A-smectic-C transition. We have studied a freestanding film of "de Vries" compound, which exhibits the smectic-A-smectic-C transition without layer shrinkage, mixed with functionalized gold nanoparticles. The tilt induced by nanoparticle clusters, which decorate the edge dislocations, has been observed in the smectic-A phase. The tilt of liquid-crystal molecules near nanoparticles is a consequence of interaction of liquid-crystalline molecules with the surface of nanoparticles. The observed tilt may prove the concept of existence of a disordered tilt in the smectic-A phase of de Vries compounds. The tilt distribution near nanoparticles is discussed using both the smectic-A elasticity and local smectic-A-smectic-C transition.
Asunto(s)
Oro/química , Cristales Líquidos/química , Nanopartículas del Metal/química , Nanopartículas del Metal/ultraestructura , Modelos Químicos , Modelos Moleculares , Simulación por Computador , Ensayo de Materiales , Conformación Molecular , Tamaño de la Partícula , Transición de FaseRESUMEN
It is shown that a smectic A droplet deposited on a solid substrate treated for strong homeotropic anchoring is faceted at the top in spite of the fact that there are no steps at the free surface, but instead edge dislocations in the bulk. The radius of the facet and the full profile of the curved part of the droplet are determined as a function of the temperature in the vicinity of a nematic-smectic A phase transition. It is shown that the observed profiles do not correspond to the actual equilibrium shape, but to metastable configurations close to their point of marginal stability. In addition, we predict that the profiles must be different for a given temperature depending on whether the droplet has been heated or cooled down to reach this temperature. Finally, we discuss the problem of the formation of giant dislocations in big droplets (Grandjean terraces).