Colloidal Silica Rods in Electric Fields; Towards a Two-dimensional System

Abstract

We studied the phase behaviour of dilute systems of colloidal rods in electric fields by confocal microscopy. Sample cells with electrodes at the bottom and top of the sample were used. The first steps towards a two-dimensional systems of rods were taken. From a combination of theory and experiments, it was concluded that obtaining an experimental two-dimensional system of rods is probably possible, provided that sufficiently large rods are used. Also, new structures were seen: at certain concentrations, pair and cluster formation of rods at the bottom layer of samples, on an electrode, were observed. The corresponding attractive behaviour is not predicted in theory. A second layer on top of the bottom layer, consisting of rods which aligned with the electric field, is expected to turn the attraction into a repulsion. By constructing a phase diagram, we showed that the necessary conditions for pair and cluster formation are delicate. We obtained an experimental system of a single layer of rods aligned in the electric field, parallel to gravity. The study of such systems of colloidal silica rods not only provides insight in the fundamental interactions between polarized particles, but has many applications in e.g. calibration samples for new microscopy techniques and photonic crystals.