Colloids are found in many industrial processes and often undergo flow. The aim of this project is to gain a greater physical understanding of how the microscopic structure of such systems changes under flow. A colloidal gel is an experimental model system made up of particles (about 1micron in size) that form a frozen, space filling network (Figure 1). Experiments are conducted using a purpose built shear cell that essentially consists of two parallel, flat plates which undergo an oscillatory movement and thereby shear the sample. The shear cell is combined with the COSMIC Biorad confocal microscope to provide images of the gel structure before (Figure 1) and after shear (Figure 2). We have developed special florescent particles for use with the confocal microscope. Using suitable imaging procedures, we have obtained high quality images of the gel structure at the particle length scale throughout the whole sample volume. We have used the Visualisation Suite to analyse images and to develop methods to determine the 3D positions of the particles.
The main outcome of this project so far is not only information on changes to gel structure under shear, but also development of the shear cell and imaging methods. The dense gel structure is found to be significantly affected by shear: The size and shape of the empty spaces within the gel network change leading to structures not normally seen in a gel. Furthermore ordered regions within the gel are formed. This implies significant rearrangement of the particles, which can by quantitatively investigated using COSMIC.