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CHANGE OF TIME FOR Special Seminar at Harvard on Monday, August 21. NOW at 11:00 a.m.

The time of this seminar has been changed:



Special Seminar at Harvard University, Paulson School of Engineering and  Applied Sciences:



Monday, August 21, 2017 at 11:00 a.m.

Harvard University

Pierce 209


“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 [3]. 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 [3].

[1]   A.L. Thorneywork, R. Roth, D.G.A.L. Aarts and R.P.A. Dullens, J. Chem. Phys. 140, 161106 (2014).
[2]   A.L. Thorneywork, R.E. Rozas, R.P.A. Dullens and J. Horbach, Phys. Rev. Lett. 115, 268301 (2015).
[3]   A.L. Thorneywork, J.L. Abbott, D.G.A.L. Aarts and R.P.A. Dullens, Phys. Rev. Lett. 118, 158001 (2017).