Colloid Science

1. Novel ("smart") colloidal systems.

   I have a major interest in the synthesis and properties of various kinds of colloidal systems, which have some designed functionality. Colloidal systems of this type are of interest, not only academically, in testing theories of colloid science, but also practically, in that they often lead to an application which industrialists can exploit. Many of the systems investigated have been based on polymer latices, and include: (a) electrically conducting particles; (b) microgel particles; (c) liquid polymer "particles"; (d) core-shell type particles.

   The electrically conducting particles have been used to test the theories of electrophoresis and electro-rheology. Their possible use in (electrically-conducting) composites and films has also been looked at. The microgel particles have been used to investigate rheology control (e.g. in oil wells) and for controlled uptake and release purposes (particularly of ions in contaminated waters). The liquid latex particles (based on polydimethylsiloxane) are being used to test various hydrodynamic theories of dispersed droplets; the big advantage here is that they are surfactant-free and monodisperse. Various types of core-shell systems have been investigated, including : polymer or silica cores with terminally-grafted, monodisperse polymer or polyelectrolyte chains (for testing the theories of interparticle interactions); liquid latex cores with hard shells (for controlled release and pressure release purposes). Recently, I have developed a new interest (with Dr. Jim Goodwin), in the area of synthetic clays.

2. Interparticle forces and dispersion stability, in particular the role of polymers.

   Polymers are widely used, in practice, to control the properties (e.g. the stability, rheology) of colloidal systems. The adsorption of polymers at interfaces and their effect on dispersion stability has been another area of work in my group, partly in collaboration with Dr. Terry Cosgrove. In many cases the (monodisperse) polymers used (homopolymers and block copolymers) have been synthesised in my laboratory using anionic polymerisation equipment. Some of the work in this area has been directly supported by Industry, recent examples being the control of stability in propellant liquids and in lubrication oils. I have been particularly interested in the role of non-adsorbing polymers, which gives rise to depletion flocculation. Weak, reversible aggregation, leading to colloidal phase separation and the thermodynamic and mechanistic aspects of this, has been a major theme. The role of electrostatic interactions in dispersions in non-polar media, has been a much-debated subject for many years. We have recently constructed equipment, based on a new method of processing light scattering data (phase-analysis light scattering), which for the first time, allows very small electrophoretic mobilities (also for small particles) to be accurately determined, by separating out the diffusion component.

3. Particle deposition / "adsorption" on macroscopic surfaces

   This topic is also important in a number of technologies, including detergency, surface coatings, printing and paper-making. We have been studying particle adsorption, under quiescent conditions, and, more recently, deposition under flow, onto a variety of surfaces. We have constructed a stagnant-point flow apparatus, linked to an image-analysis system, for looking at the spatial distribution of deposited particles. We have acquired an atomic force microscope, to monitor the direct interaction of particles (attached to the "tip") with the substrate. We are currently constructing a total internal reflectance microscope and "flow-through" cells to investigate particle removal from (rewetted) surfaces. The interaction of particles with gas bubbles is a related area, important in flotation and detergency, which we are studying.