Sommaire:

While systems of uniform particles (colloids, nanoparticles, atoms) and discrete mixtures (binary, ternary) have traditionally been well studied, much less is known about particles with a continuous distribution in sizes and shapes. Such disperse particle systems are natural outcomes of syntheses or can develop dynamically through exchange of mass or charge or mechanical forces between neighboring particles. Theoretical research over the last 20 years pointed towards a fractionation mechanism involving multiple face-centered cubic crystals with narrower size distributions in each crystal than the size distribution of the fluid. However, experiments were unable to confirm such a behavior. Only recently, first evidence appeared that dispersity can be responsible for novel crystallization phenomena. We confirm this view with the help of computer simulations of a simple model system – size-disperse hard spheres [1]. We can now unambiguously state: particles with dispersity eventually do crystallize, even for high values of dispersity, and they do so in unexpected ways. Our findings suggest that crystallization of size-disperse colloids closely mimics crystallization in binary mixtures into AB2 and AB13 crystals and alloys by favoring Frank-Kasper phases. We obtain this result with the help of an algorithm that combines event-driven molecular dynamics with particle swap move (static dispersity) or particle resize moves (dynamic dispersity).

Reference:
[1] P.K. Bommineni, N.R. Varela-Rosales, M. Klement, M. Engel, Complex Crystals from Size-Disperse Spheres, Phys. Rev. Lett., in press (2019).

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