Self-assembly of colloids with anisotropic shape and interactions

Abstract

In this thesis the self-assembly of anisotropic polystyrene colloidal particles is studied using optical microscopy. These particles consist of different lobes with attractive and non-attractive interactions. This anisotropy in inter particle interaction is induced by depletion attraction combined with a difference in surface roughness between the lobes. The shape of the particles that are used as building blocks has a profound effect on the structures formed by self-assembly. Snowman or dumbbell-shaped particles consisting of one attractive (smooth) and one non-attractive (rough) lobe self-assemble into spherical micelle-like structures. These particles can also be used to encapsulate and stabilize larger spherical particles. Triangular particles on the other hand, consisting of one attractive and two non-attractive lobes, resembling a “Mickey Mouse” head, self-assemble into elongated tube-like structures. These structures are observed with optical microscopy in the experimental system and supported by Monte Carlo simulation results. Understanding this effect of building block shape on the resulting structure is important for the design of building blocks for the formation of new, functional structures by self-assembly. These structures could for instance be used as vehicles for targeted drug delivery. The geometry of dumbbell-shaped particles also has an effect on the crystalline ordering of these particles by convective assembly. A larger particle length (less overlap between the lobes) results in reduced crystalline order, while crystals of these particles have interesting optical properties with possible application as photonic crystals.