Active Anisotropic Colloids from Colloidal Monolayers

Abstract

In this thesis we describe several colloidal model systems. We first study the lattice structures in monolayers of colloidal superballs prepared using the unidirectional rubbing method. In this method, the ordering of the colloidal superballs is achieved by mechanically rubbing them onto a polydimethylsiloxane- (PDMS) coated surface. We show using both small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) that a transition in the lattice structures result from a well-defined hexagonal lattice for spherical superballs to the sliding phase for more cube-like superballs. In these lattice structures the cube-like superballs form chains in the direction in which the mechanical rubbing was applied which are able to slide freely with respect to each other. Furthermore, we show that active colloids with an asymmetrically sputter coated metal patch display circling motion under the influence of an alternating electric field. Their velocity and angular velocity can be tuned in situ by varying the magnitude and frequency of the alternating electric field. Finally, we present a method to prepare active anisotropic hydrogel particle. Using this simple and accesible method, particles with an arbitrary geometry and tunable thickness can be prepared which display an active motion under the influence of an alternating electric field.