Résumé:

In a seminal work, [1] D. R. Nelson proposed that nematic coatings could be used to promote localized functionalization on colloidal particles. Topological defects are indeed necessarily present on genus-0 surfaces and it could be possible to attach ligands to them. Such a realization, however, still remains an experimental challenge. As a first step, the fabrication of thin nematic shells from double emulsions drops was reported a few years ago in Ref. [2]. Since then, the equilibrium structure of the topological defects on a sphere has been studied in details both theoretically and experimentally. It not only depends strongly on the homogeneity of the shell thickness [3,4] but also on the nematic elastic constants [4,5]. The defects structure on a nematic shell can therefore be finely controlled. As a next step, we have recently examined, both experimentally and theoretically, how a small number of solid particles can be trapped on nematic shells[6]. We have used water/5CB/water double emulsions produced by microfluidics techniques. The anchoring of the nematic at the water-5CB interface is strongly planar due to the presence of polyvinyl alcohol in aqueous solutions. The colloids are silica beads treated with silane to provide a homeotropic alignment. We especially have examined how the particles interact with the topological defects, where they get trapped, and how the equilibrium textures depend on their size. A great diversity of defect structures and patterns, different from the ones known in simple nematic shells, can be observed. I will describe their main features and explain how they result from the competition between elasticity and capillarity effects, during the formation of the shells. I will show how this last mechanism can be used to control the position of ligands on a spherical shell.