The 2009 Dirac medal went to  Professor Michael Cates for his pioneering work in the theoretical physics of soft materials, particularly in relation to their flow behaviour. Distinguished for his research into the statistical mechanics of soft materials, such as polymers, emulsions, colloids, foams and liquid crystals, these show mesoscopic structure which can lead to startling flow behaviours: viscoelasticity, jamming, and flow-induced phase transitions.

Cates has played a leading role in the creation of statistical-mechanics models to explain such phenomena. He developed a model for entangled polymer-like objects that can break and recombine reversibly, explaining the flow of behaviour of a class of viscoelastic surfactant solutions, in products ranging from shampoo to oil-bore fluids. He co-invented models for the isotropic ‘sponge phase’ of surfactants, identifying its structure and explaining its reversible conversion into a liquid crystal under shear. With Milner and Witten, he created a theory of polymer chains coating a surface by attachment at one end - the ‘polymer brush’.

Cates’ major interest subsequently has been in modelling the flow of soft materials not in equilibrium, even at rest. His work has caused many such materials (shaving foam, mayonnaise, wet corn starch) to be viewed as ‘soft glasses’, with distinctive properties stemming from their structural arrest.

With Fuchs and others, he developed first-principles treatments of the flow of dense colloidal suspensions, building on modern theories of glass transition. Another achievement has been to accurately simulate the demixing of binary fluids, and then study its arrest by colloidal particles leading  directly to the creation of new functional materials (‘bijels’) in the laboratory.

His work exemplifies how cutting-edge theoretical physics impacts, not only  other disciplines such as chemical engineering and materials science, but on readily observable domestic phenomena such as tomato ketchup failure to come out of the bottle.

The 2009 Payne Gaposchkin medal and prize goes to Professor Eric Priest for his numerous major contributions to many of the unsolved problems in solar physics, including magnetic reconnection, coronal heating, phasing-mixing of MHD waves and solar flares.

Priest is a world leader in solar physics, building up a Solar Magneto-hydrodynamics (MHD) Group at St Andrews University to a group of eight permanent staff, six postdoctoral researchers and 15 research students. Thirty-four former group members now hold tenured university teaching positions.

His research focussed on the fundamental physical processes at work in the solar corona. Often driven by new outstanding observations, he provided the community with a theoretical description of many solar phenomena, such as coronal heating mechanisms through both the damping of MHD waves and the dissipation of many small-scale current sheets. His work on magnetic reconnection, in 2D and in 3D, has been a driver for a worldwide effort on this complex topic.

His monograph, “Solar MHD”, is the recognised textbook for all researchers in theoretical solar physics and  translated into Russian and Chinese. He also co-authored “Magnetic Reconnection” a a comprehensive summary of all aspects of the fundamental physical processes of magnetic reconnection.

The Young Medal and prize go to  Professors Leslie Allen (right) and Miles Padgett  (below left) In recognition of their pioneering work on optical angular momentum.Kepler deduced from the sun’srole in shaping comets’ tails that light carries linear momentum.

Mathematically embedded in Maxwell’s equations, it is only recently, thanks to the seminal work of Allen and Padgett that researchers have recognised and taken advantage of the full properties of light’s angular momentum.

Beth showed that light carried spin angular momentum, but it was not until 1992 that light’s orbital angular momentum was elucidated by Allen and co-workers. Since then Allen and Padgett have pioneered both theoretical and experimental approaches to investigate virtually all aspects of light’s angular momentum.

They succeeded in converting optical tweezers into optical spanners, using light to rotating microscopic objects; showing the mechanical equivalence of light’s spin and orbital angular momentum which has inspired much work in optical manipulation.

Earlier there had been a study of this light’s interaction with atoms. Working together,they recognised the role that light’s orbital angular momentum plays in harmonic generation; a precursor to high-dimensional quantum entanglement.

The phenomenology of orbital angular momentum encompasses geometric phases, rotational Doppler shift, angular uncertainly relationships and other topological features. It has been demonstrated that spin, orbital and total angular momentum can be measured for single photons and the increased data capacity utilised in a free space optical link.

2009 IOP Awards