Function Follows Form : Geometric Effects in Colloidal Self-Assembly

Abstract

In the microscopic world of self-assembly, function follows form. Driven by their ever-present random Brownian motion, colloids (particles between 1 nm and 1 μm in size) suspended in a fluid can assemble themselves into complex structures. Which structure is formed follows from the properties of the colloids and the interactions between them. For solid colloids, a key property is their shape. When self-assembling, the shape of the particles and the geometry in which the self-assembly takes place are what determine the geometric arrangements that the particles can take on. This arrangement, in turn, determines the large-scale properties of the self-assembled structure, such as the wavelengths of light it interacts with, or the ways in which it can bend or break.

This thesis uses computer simulations to shed light on the link between shape and structure in four separate scenarios. Firstly, we show that for self-propelled particles a non-spherical shape induces torques that can inhibit the commonly found motility-induced phase separation. Secondly we study hourglass-shaped particles adsorbed at a fluid-fluid interface, and find that the self-assembly is dominated by shape-specific capillary interactions that arise from the anisotropic particle shape. Third, we demonstrate the wealth of crystal structures that can be attained by careful tuning of the shape of rounded tetrahedral particles, and how to tame this complexity of structures. And lastly, we show that when confining such rounded tetrahedral particles to self-assemble within an evaporating fluid droplet, knowing the bulk structures is not enough, as in such confined systems completely new structures can arise.