Two-dimensional (2D) systems give rise to phenomena that are often unexpected and very different to their 3D counterparts, an observation that has led to the recent explosion in technologies exploiting the remarkable properties of 2D materials, such as graphene. Yet understanding the microscopic origins of this superlative behaviour is extremely challenging.
In seeking to understand materials composed of many particles, we often look to the simplest possible realisation, and in condensed matter physics the most fundamental many body systems are so-called ‘hard spheres’; particles that exhibit only an excluded volume interaction. While hard spheres have been studied extensively in theory and simulation, their experimental realization is more challenging, however colloidal suspensions have long been recognised as one of the best experimental models of this system.
Colloidal monolayers have recently been recognised as exceptional two-dimensional hard sphere (hard disk) model systems, allowing for the statistical mechanics of these systems to be studied in detail. Most notably this led to the first experimental elucidation of the two-dimensional melting of hard disks, thereby solving one of the longest-standing problems in condensed matter physics.
Alice L. Thorneywork, Roland Roth, Dirk G. A. L. Aarts and Roel P. A. Dullens, ‘Radial distribution functions in a two-dimensional binary colloidal hard sphere system’, Chem. Phys. 140, 161106, (2014)
Alice L. Thorneywork, Roberto E. Rozas, Roel P.A. Dullens, Jürgen Horbach, “Effect of hydrodynamic interactions on the self-diffusion of quasi-two-dimensional colloidal hard spheres”, Phys. Rev. Lett., 115, 268301, (2015)
Alice L. Thorneywork, Joshua L. Abbott, Dirk G. A. L. Aarts and Roel P. A. Dullens, ‘Two dimensional melting of colloidal hard spheres’, Phys. Rev. Lett, 118, 158001, (2017)