Colloidal crystal growth

Abstract

The growing process of localised ordered structure near a smooth glass plane has been studied by using an optical microscope (used as an ultramicroscope) and a video image analyser. During the observation, in order to obtain more reliable data on crystallisation than previously, the temperature was carefully controlled and 4000–10 000 particles were treated by modern image data processing. The growth of the structures was studied using 2D-Fourier analysis of the information of particle coordinates (density function). The effect of the sedimentation of the particles on the growing process was confirmed to be negligible by density-matching experiments with a D₂O–H₂O mixture. The time evolutions of the numbers of particles, structure units and clusters were followed. The number of clusters consisting of relatively few particles (3–10 particles) first increased with time and then decreased, while those consisting of many particles (>20 particles) simply increased. The larger clusters grew at the expense of smaller ones in conformity to the Ostwald ripening mechanism, confirming the existence of a long-range attraction between latex particles. The 2D radial distribution function was determined directly from the particle coordinates at various stages of crystallisation, from which the evolution of number of the nearest-neighbour particles was demonstrated. The growing process could be divided into four stages. In the first stage, the motion of the particles was not restrained. In the second stage, the interaction between the particles determined the concentration and arrangement of the particles. In the third stage, stable clusters were formed. In the last stage, rearrangement of the clusters was observed and the near-perfect ordered structure was formed. The first three stages were slow at lower particle concentrations.