Structure formation of anisotropic particles interacting via critical Casimir forces

Abstract

This thesis presents hierarchical assembly of semicircle colloids induced by critical Casimir forces. Recent experiments demonstrated how assembly takes advantage of the fact, that the strength of such forces strongly depends on the temperature of the fluid and the adsorption preference of the colloidal particles. Here, in contrast, the curvature dependence of critical Casimir forces is exploited to guide the assembly. As far as known, this has not been studied before. A preferential attraction between the flat facets of the particles which leads to their assembly into disk-shaped aggregates is observed. This disks then aggregate further on to larger structures. The interaction potentials are measured for different curvatures by optical microscopy and compared to simulations of van der Waals forces, which show a similar shape dependence. Starting from that, different possible protocols to attain hierarchical assembly are presented. Although the initial goal, to form large colloidal crystals, has not been reached, the results suggest that such ordered structures are achievable on further optimisation.