Elastocapillarity in thin nematic liquid crystal films: the interactions between colloidal particles
Résumé
The confinement of colloidal particles in thin liquid films is typically accompanied with interfacial deformations which give rise to long-range capillary forces, attractive in most of the cases [1]. In simple fluids, these long-range capillary forces compete mostly with the isotropic electrostatic interactions. In nematic[2] or smectic[3] liquid crystal free films, other long-range anisotropic interactions related to bulk distortions of the surrounding fluid appear and new equilibrium positions or the possibility of forming new types of 2D colloidal assemblies appear via original elasto-capillarity couplings.
In a previous work [4], using spatially resolved retardation and easy-axis maps, we have analysed quantitatively the 2D interfaces deformation and the nematic textures observed around isolated particles (see Fig.1) embedded in thin nematic films with hybrid anchoring conditions. Using numerical methods, we have explained quantitatively the different textures and the formation of topological defects. Contrary to what is classically observed in aligned nematic cells, the equilibrium patterns (such as the elastic dipole) due to a microsphere can be much larger than the particle size (as shown in Fig.1).
Here we have focused on the overall colloidal interactions and the equilibrium positions between spherical or anisotropic particles. We have experimentally characterized the equilibrium configuration of isolated colloidal pairs. Using a 2D model of the nematic elasticity and finite element approaches, we have also numerically characterized the pair interaction and explained the textures observed. These new spontaneous organizations in thin nematic films offer new ways to self-assemble complex colloidal systems in 2D.
References
[1] P.A. Kralchevsky, K. Nagayama, Adv Colloid Interface Sci , 85, 145 (2000).
[2] H.Jeridi, M.A.Gharbi, T.Othman, Ch.Blanc, Proc Natl Acad Sci USA, 112, 14771(2015).
[3] M.A.Gharbi et al., Langmuir, 34, 2006 (2018).
[4] H. Jeridi, M. Tasinkevych, T. Othman, and Ch. Blanc, Langmuir, 32, 9097 (2016).