Electrostatic manipulation of colloidal clusters

Abstract

In this thesis, we show that external electric fields can be used to manipulate clusters of colloidal particles. A cluster of particles can be expanded in a controlled fashion, can be arranged in a ring, and can have a negative Poisson’s ratio if there is significant anisotropy in the particle interactions. The induced electric forces on the particles depend on the electric field and can be determined experimentally by the particle position. An electric field induces an electric dipole moment in metallic and dielectric media if there is a difference in dielectric constant between an object and its surrounding. It is shown that the induced electric dipole moment can be used in various ways to manipulate colloidal particles. In this thesis, two set-ups are discussed to manipulate colloid clusters with an induced electric force. In the first set-up, the particles are adsorbed on a curved water-oil interface in an electric device. While the curved interface promotes particle movement towards the lowest position on the interface, the electrically induced forces act against the movement in this direction. This provides a method to control the position of the particles. In the second part of this thesis, the particles contain a permanent magnetic dipole moment, which causes the particles to cluster into a rhombic-like structure. An induced electric dipole moment causes repulsion between particles, this breaks up the rhombic-like structure and causes the cluster to expand. When considering the cluster as a material, this material has a negative Poisson’s ratio.