Confining a smectic liquid crystal between two spherical surfaces results in the formation of a complex defect structure characterized by a set of curvature walls that divide the sphere into crescent domains, causing the undulation of the smectic layers. In this paper, we examine in detail these smectic textures and discuss the various possible origins of the observed patterns.

We show that single-wall carbon nanotubes (SWCNT) can be dispersed as individuals in poly(vinyl alcohol) matrix composites up to concentrations of 1 wt %, as indicated by their strong photoluminescence (PL) signal in the near-infrared all along the processing steps. The alignment of the SWCNT is controlled by hot-stretching of the composite films. We show that orientational order can be described accurately from polarized Raman and PL spectroscopies, in good agreement with a simple affine model, providing their anisotropic absorption is properly taken into account. Similar results are obtained from different excitation laser lines (in the visible and near-infrared), confirming that all nanotubes orient the same way.

In order to investigate the coupling between the degrees of alignment of elongated particles in binary nematic dispersions, surfactant stabilized single-wall carbon nanotubes (CNTs) have been added to nematic suspensions of colloidal rodlike viruses in aqueous solution.We have independently measured the orientational order parameter of both components of the guest-host system by means of polarized Raman spectroscopy and by optical birefringence, respectively. Our system allows us therefore to probe the regime where the guest particles (CNTs) are shorter and thinner than the fd virus host particles. We show that the degree of order of the CNTs is systematically smaller than that of the fd virus particles for the whole nematic range. These measurements are in good agreement with predictions of an Onsager-type second-viral theory, which explicitly includes the flexibility of the virus particles, and the polydispersity of the CNTs.

We study nematic shells with four s=+1/2 defects and vary the elastic constant anisotropy of the liquid crystal by approaching the nematic-to-smectic phase transition temperature. We find the defects ultimately arrange themselves along a great circle, consistent with recent expectations. Changing the elastic constant anisotropy provides an alternative route to changing the shell thickness inhomogeneity for controlling the defects location.

An assembly of packed and oriented rodlike particles exhibit anisotropic physical properties. We investigate in the present work the anisotropic conductivity of films made of intrinsically conducting rods. These films are obtained from more or less ordered carbon nanotube liquid crystals. Their orientational order parameter is measured by polarized Raman spectroscopy. A relationship between the anisotropy of surface conductivity and orientational order parameter is determined. The experimental results are accounted for by a model that takes into account the number of intertube contacts and density of conductive pathways in different directions, as introduced by J. Fischer et al. for magnetically aligned nanotubes. We find that a good agreement, without any fitting parameter, of the proposed model and experiments is obtained when we consider a two-dimensional (2D) Gaussian distribution of the nanotube orientation. The conductivities parallel and perpendicular to the nematic director differ by almost an order of magnitude. This anisotropy is much greater than that of conventional dielectric liquid crystals, where the behavior is governed by the mobility anisotropy of ionic current carriers. The present results do not depend on the intrinsic properties of the nanotubes and are expected to be relevant for other assemblies of conducting rodlike particles, such as metallic or semi-conducting nanowires and ribbons.

We present in this Rapid Communication experimental evidence of an acceleration of the zenithal easy-axis dynamics of a nematic liquid crystal (NLC) with the age of a NLC-polymer layer. The comparison with other hard alignment layers strongly indicates that the polymer softness and its ability to reorient in the nematic ordering field is at the origin of the measured dynamics. The unusual acceleration of the dynamics with the polymer age is discussed in terms of this unique coupling with the NLC order. The NLC behaves like a physical plasticizer as a result of the coupling between the NLC and the polymer orders.

Le confinement et la courbure ont généralement des effets dramatiques sur les systèmes ordonnés tels que les cristaux liquides. Une de leurs principales conséquences est l’apparition de défauts topologiques qui altèrent localement l’ordre moléculaire du système. En particulier, quand un nématique est confiné dans une coque sphérique, une configuration avec quatre défauts organisés de manière tétraédrique est prédite [1]. Ces défauts pourraient être fonctionnalisés afin de créer des colloïdes tétravalents, ce qui permettrait de reproduire à l’échelle micrométrique la structure type diamant du carbone, un des défis actuels de la photonique. Malgré l’intérêt suscité par cette prédiction théorique, l’ordre nématique dans les coques sphériques n’a que peu été exploré expérimentalement. Ici, nous étudions les différentes structures des défauts observés expérimentalement dans des coques nématiques. Les coques étudiées sont des émulsions doubles générées par des techniques de microfluidique [2, 3]. La phase du milieu est un cristal liquide thermotropique, 4-n-octyl-4-cyanobiphenyl (8CB), alors que les phases intérieure et extérieure sont des solutions aqueuses contenant de l’alcool polyvinylique (PVA) qui stabilise l’émulsion double et force un ancrage planaire. En plus d’observer la structure tétraédrique originalement prédite par la théorie, nous montrons que cette structure n’est qu’une des nombreuses configurations résultant de la variation de l’épaisseur des coques [4]. Cette richesse dans la palette des configurations observées est multipliée lorsqu’on introduit, par l’intermédiaire de la température, une anisotropie entre les constantes élastiques K3 (flexion) et K1 (ébrasement) du cristal liquide. Une divergence du ratio K3/K1 empêche énergétiquement les distorsions de type flexion. En conséquence, les défauts se réorganisent autour d’un grand cercle de la sphère, confirmant ainsi les résultats récents des simulations [5]. Lorsque 1