Special Seminar at Harvard University, Paulson School of Engineering and Applied Sciences:
Monday, August 21, 2017 at 2:00 p.m.
“Two-Dimensional Melting of Colloidal Hard Spheres”
Professor Roel Dullens
University of Oxford, Physical and Theoretical Chemistry Laboratory
Abstract: 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. Here, 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).