By: Nuno Silvestre
From: CFTC - Universidade de Lisboa
At: Instituto de Investigação Interdisciplinar, Anfiteatro
Colloidal crystals belong to a new class of materials with unusual properties in which the big challenge is to grow large scale structures, of a given symmetry, in a well controlled and inexpensive way. Template-assisted crystallization was successfully obtained experimentally in the case of colloidal particles dispersed in isotropic fluids. It has the advantage (i) of driving the formation of new structures through the symmetry of the template, and (ii) of growing colloidal structures that are less defective and possess long range structural order. Given their electro-optical and mechanic response, liquid crystal nematic colloids, where the dispersed particles exhibit long-range anisotropic interactions, have been proposed for application in photonic crystals, for which controlling the symmetry of the colloidal assembly is very important. Here we revisit the main characteristics of nematic colloids focusing on their pair-wise interaction and how it determines the formation of large colloidal structures. We discuss the behavior of colloidal particles in the presence of topographic patterns, comparable to the size of the particles. We show the existence of strong trapping potentials that are able to efficiently localize the colloidal particles and withstand thermal fluctuations. Finally, we discuss how topographically patterned surfaces can be used to guide the assembly of large colloidal structures in nematic liquid crystals.