Joan van der Waals colloquium
- Roel Dullens (University of Oxford)
- Friday 16 February 2018
- Drinks afterwards.
Niels Bohrweg 2
2333 CA Leiden
- De Sitterzaal
Two-dimensional melting of colloidal hard spheres
Despite the recent interest in the novel and unique properties of two-dimensional materials, the melting behaviour of the simplest two-dimensional material, hard disks, is still intensely disputed. Crucially, until now – more than half a century after the first simulations of hard-disk freezing were published – no reliable experimental observations of the phase diagram of two-dimensional hard spheres have been reported.
In this talk, I will describe how we determine the full phase behaviour of quasi-two-dimensional colloidal hard spheres [1, 2] by considering a tilted monolayer of particles in sedimentation-diffusion equilibrium . In particular, we measure the equation of state from the density profiles and use time-dependent and height-resolved correlation functions to identify the liquid, hexatic and crystal phases. We find that the liquid-hexatic transition is first order and that the hexatic-crystal transition is continuous. Furthermore, we directly measure the width of the liquid-hexatic coexistence gap from the fluctuations of the corresponding interface, and thereby experimentally establish the full phase behaviour of hard disks .
 A.L. Thorneywork, R. Roth, D.G.A.L. Aarts and R.P.A. Dullens, J. Chem. Phys. 140, 161106 (2014).
 A.L. Thorneywork, R.E. Rozas, R.P.A. Dullens and J. Horbach, Phys. Rev. Lett. 115, 268301 (2015).
 A.L. Thorneywork, J.L. Abbott, D.G.A.L. Aarts and R.P.A. Dullens, Phys. Rev. Lett. 118, 158001 (2017).