This work represents a pioneering combination of polymer chemistry, physics and colloid science. We have prepared tiny particles that at low temperature are little "rods" but which change shape to become spheres at higher temperature [Yang et al.(2005)]. On cooling they revert to being ellipsoidal again. This reversible shape change can also be achieved using other triggers. Potential applications include electro-rhelogical fluids, microfluidic gates, responsive mirrors.
Plugging the gap
Deformation of emulsion droplets in drilling muds
When oil companies drill for oil a "drilling mud" is used to perform several important tasks, one of which is to form a filter cake on the side of the well bore against the rock formation. This filter cake can prevent loss of drilling fluid to the rock and also act as a way of stabilizing the rock formation preventing it from crumbling. This area of our work involves emulsion droplets (a bit like mayonnaise!) with a narrow size distribution to prepare filter cakes so that the key factors (viscosity, surfactant nature, etc.) that most effect the permeability of the cake can be determined and compared with modelling predictions [Headen et al.(2006)].
Microgels are polymer colloids that respond to an external trigger to expand in size. They have been used extensively as rheological modifiers and as controlled release agents.
We have examined the thermodynamics of the swelling step and the effect of free polymers that induce a further swelling by infusing into the particle [Routh et al.(2006)]. The fluid mechanics of flow through and round the swollen particles and the dynamics of swelling, which is hydrodynamically controlled, have recently been examined. In addition the bulk rheological behaviour through the swelling transition displays a colloidal instability and a resulting jump in the dispersion viscosity.
Yang, Z.Q., Huck, W.T.S., Clarke, S.M., Tajbakhsh, A.R. and Terentjev, E.M. (2005) Shape-memory nanoparticles from inherently non-spherical polymer colloids. Nature Materials 4, 486-490.
◾ Headen, T.F., Clarke, S.M., Perdigón, A., Meeten, G.H., Sherwood, J.D. and Aston, M. (2006) Filtration of deformable emulsion droplets. J. Colloid and Interface Science 304, 562-565.
◾Routh, A.F., Nieves, A.F., Bradley, M. and Vincent, B. (2006) Effect of free polymer on the swelling of neutral microgels: a thermodynamic approach. J. Phys. Chem. 110 (25), 11721-12727.