News: Summer 2008, with Stephen Williams and Hajime Tanaka, we publish the first direct experiment evidence of a structural mechanism for dynamical arrest: read all about it at the UoB press release, the New Scientist, Nature research highlights, Physics world (for those fortunate enough to have access...) and many more. A 'German translation' is also provided.

"Crystallization of Dense Binary Hard-Sphere Mixtures with Marginal Size Ratio," with Stephen Williams and Gary Bryant published in Physical Review Letters 100, 225502 (2008), is selected for the June 16, 2008 issue of Virtual Journal of Nanoscale Science & Technology Nanoscale Science & Technology.

What's the game all about?
Colloidal dispersions allow us to tackle some of the most challenging and fundamental unsolved physical problems that surround us in everyday life. How do solids melt? How do liquids freeze? Why, when we cool silicon dioxide (or a host of other materials) does it form glass, not quartz? Perhaps amazingly, at the dawn of the 21st century, these problems remain unsolved. Why?
The answer in a nutshell is that atoms or molecules are too small to be seen, and that, in order to answer these questions, we need to be able to see them. So how is this resolved? Enter colloidal dispersions: we take micron-sized particles, which, crucially, are big enough to resolve in an optical microscope, yet small enough to exhibit thermal Brownian motion, as shown in the movie above. What this leads to that colloids obey the same laws of statistical mechanics that atoms and molecules do, and so, like atoms and molecules, they for gases, liquids and solids. Unlike atoms we can see them easily in a microcope, and thus, by looking at colloids, and understanding the local phenomena which control their freezing, melting and vitrification, we are simultaneously answering the same questions about atoms and molecules.

Dynamics
However colloids are not simply big atoms, they are suspended in a solvent. The many-body long-ranged hydrodynamic interactions mediated by the solvent present a deeply challenging fundamental problem, which we can begin to unravel with high-quality imaging. Perhaps the most obvious question is, how do colloids settle under gravity?