Résumé
Liquid crystal (LC) colloidal dispersions have been shown to promote complex ordered organizations due to the local distortion of the host by the particles and the resulting long-range elastic interactions mediated by the Frank elasticity. The key components responsible for these colloidal patterns have been well understood at the micron scale and are now increasingly studied at the sub-micron scale. One of the main challenges in order to design useful colloidal dispersions in a nematic however remains the fine control of the multipolar elastic interactions. The attractive components are indeed usually sufficiently strong to lead to a rapid aggregation of dispersed particles. We will first discuss some strategies to prevent this phenomenon in bulk.
We will also discuss the case of particles trapped at liquid crystal interfaces where the elastic interactions are strongly modified by the confinement [1,2] but also might compete with capillary interactions, as we detailed recently [3]. When confined at LC interfaces, spherical particles with homeotropic anchoring interact with repulsive interactions only, then forming regular arrays with large lattice parameters. When they are confined in a thin nematic film the colloidal behaviour is much more complex depending on the boundary conditions at the interfaces. For example we have shown that the capillary attraction expected for particles confined in thin films with hybrid anchorings is counteracted by the nematic texture and the presence of topological defects.
[1] M.A. Gharbi, M. Nobili, M. In, G. Prévot, P. Galatola, J.-B. Fournier, and Ch. Blanc, "Behavior of colloidal particles at an air/nematic liquid crystal interface", Soft Matter, 7, 1467-1471, (2011).
[2] M. A. Gharbi, M. Nobili, Ch. Blanc, "Use of topological defects as templates to direct assembly of colloidal particles at nematic interfaces",J. Colloid. Interface Science, 417 ,250 (2014).
[3] Jeridi Haifa, Gharbi M. A., Othman Tahar, and Blanc C., "Capillary-induced giant elastic dipoles in thin nematic films", PNAS, 112 , 14771–14776 (2015).