Wilson Poon SRC Senior Research Fellow & Professor of Condensed Matter Physics SUPA and School of Physics The University of Edinburgh, United Kingdom

Wilson Poon is Professor of Condensed Matter Physics, with the Soft Condensed Matter research group at the University of Edinburgh.

Research Interests
Soft condensed matter physics studies liquids, called ‘complex fluids’, which contains entities with sizes intermediate between small molecules (e.g. H2O) and macroscopic objects (e.g. the beaker holding the liquid): colloidal suspensions, polymers and aggregates of surfactants (soap-like molecules). These ‘mesoscopic’ entities are dominated by thermal fluctuations (= Brownian motion). Their presence confers a host of fascinating (and highly applicable) properties to complex fluids. For instance, their response to mechanical stress is intermediate between that of the ideal solid (‘elastic’ response) and the ideal (simple) liquid (‘viscous’ response): complex fluids are ‘viscoelastic’. A good example is ‘non-drip paint’ (a complex mixture of colloids and polymers). Under the high shear stresses generated by a paint brush, it behaves like a liquid; once the painting motion stops, gravity causes a small enough stress that the paint behaves like a solid, and stays on the wall.

I mainly work on colloids - suspension of solid particles in liquids. My main interest is to use very well-characterised suspensions to throw light on phenomena that are ubiquitous throughout condensed matter physics, such as crystal nucleation. A very brief introduction to this research philosophy, sometimes dubbed ‘colloids as big atoms’, is given here. In the past I have studied equilibrium phase transitions and phase transition kinetics. A movie (taken by Dr. Falk Renth) showing a colloidal suspension separating into coexisting colloidal gas (top), liquid (middle) and crystal (bottom: iridescence caused by Bragg reflections) phases can be seen here. Now I concentrate on long-lived metastable states (glasses and gels) in the same suspensions, especially how they flow in simple and complex geometries. A very brief introduction to colloidal glasses is given here.

My main research tool is advanced optical microscopy, especially fast confocal microscopy that allows us to track thousands of particles more or less ‘in real time’, and ‘optical tweezers’, which permits the ‘hands-free’ trapping and manipulation of colloids using highly-focussed laser beams. A movie (courtesy of Dr. Rut Besseling) showing (about 3000) particles in a sheared colloidal glass reconstructed from stacks of confocal micrographs can be seen here. Most of the facilities I use are housed in COSMIC.

Speaking in the special symposium on Nanoparticles in Soft Materials - Colloidal Systems.