Patchy colloids with orthogonal functionality

Abstract

Colloidal particles are defined as objects with at least one dimension in the size range of approximately a few nanometers to a few micrometers. The analogy between colloids and molecules is applied to bridge the gap between atomic and molecular world to structured materials. A wide range of structures can be self-assembled from building blocks of different shapes, components and functionalities. However, directional forces are required for programmable self-assembly of colloids into complex hierarchical architectures. Directional interactions can be achieved experimentally via chemical patches, the combination of particle shape and depletion forces, or through capillary interaction at the liquid-liquid interface. In this thesis, we aim to develop anisotropic particles that can be used for directional assembly. This thesis is organized in two parts. In the Part 1, consisting of Chapter 2-4, we focus on the synthesis of patchy particles with orthogonal functionality and with anisotropic shapes. First, we develop a new approach based on a modified two-step seeded dispersion polymerization to prepare patchy spheres with orthogonal patches. The resulting particles feature tunable patch ratio, and chemically orthogonal handles for further chemical modification (Chapter 2). Next, we extend the patchy particles to anisotropic shape. In Chapter 3 we report a general route towards anisotropic patchy particles by combining seeded dispersion polymerization and seed mediated heterogeneous nucleation. By varying the hydrophobicity of the seeds, we could achieve anisotropic particle with the shape of snowman, dumbbells and trimers etc. (Chapter 3). Then our attention turns towards another type of colloids, dimpled particles. We present a facile method to prepare dimpled particles using seeded dispersion polymerization and propose a new mechanism to prepare dumbbell shaped particles with a transition from solid dumbbells to dumbbells with a cavity at the protrusion site. (Chapter 4). In Part 2, we transfer patchy particles to liquid-liquid interfaces to investigate how active and passive patchy particles behave at the confined environment. First, we show that the capillary interaction between Janus dumbbells is induced by both shape and chemical heterogeneity of the dumbbells. By controlling the geometry and the difference in surface hydrophobicity between two lobes of the Janus dumbbells, we could vary the configuration at the interface and the evolution of the self-assembled micro-structures (Chapter 5). Finally, we investigate the behavior of active Janus spheres at a two-dimensional liquid-liquid interface with hexagonal polystyrene lattice as obstacles (Chapter 6).