Molecular dynamics study of colloidal quasicrystals

Abstract

Colloidal quasicrystals have received increased interest recently due to new insight in exploring their potential for photonic materials as well as for optical devices [Vardeny et al., Nat. Photonics, 2013, 7, 177]. Colloidal quasicrystals in aqueous solutions have been found in systems of micelles with impenetrable cores [Fischer et al., Proc. Natl. Acad. Sci. U. S. A., 2011, 108, 1810]. A simple model potential for micelle-micelle interaction is the step potential, which is infinite for core overlaps and constant for shell overlaps. Dotera et al. performed Monte Carlo simulations of the step potential model and found quasicrystals for specific values of the packing fraction η and the shell-core ratio λ [Dotera et al., Nature, 2014, 506, 208 ]. However, the overlap of real micelles causes repulsive forces, which increase with decreasing core distance. We consider this by introducing a novel model potential with repulsive forces depending on a third parameter α. In a systematic manner we study this more realistic potential with two-dimensional molecular dynamics simulations. For α = 0 the model is similar to the step potential model. For the first time, we provide a comprehensive overview of crystalline, quasicrystalline, and disordered structures as a function of η and λ. Simulations performed with α > 0 show the impact of the repulsive forces. We find that quasicrystalline structures at high densities vanish while new quasicrystalline structures appear at intermediate densities. Our results help to tailor colloidal systems for today's advanced applications in photonics and optical devices.

Complex crystalline structures in a two-dimensional core-softened system

“…In accordance with Refs. [58][59][60]71 , tiling provided by squares and regular triangles can lead to the formation of a high-density quasicrystal with 12-fold symmetry (HD12 phase). For this reason, we calculated the form factor and χ m parameter for the structures obtained in our MD simulations.…”

Two-dimensional mixture of amphiphilic dimers and spheres: Self-assembly behaviour

“…The broad interest in 2D colloidal models is witnessed by a flourishing literature on this topic, aimed at exploring routes to self-assembly into structures of assigned morphology. In most cases, particles have been modeled either through repulsive pair potentials [28][29][30][31][32][33] or as patchy particles, [34][35][36][37][38] both being known for giving stable cluster phases at moderate temperatures. Often, the focus has been on the possibility to create quasicrystalline solids by spontaneous aggregation of the particles; in one instance, 39 the solid phases of a 2D mixture of disks and patchy particles have been analyzed, reporting the existence of many crystalline and quasicrystalline patterns; on the other hand, in a just published paper, 40 a mixture of Janus particles and much smaller disks has been studied for increasing densities, highlighting the existence of an intermediate gel-like regime.…”

Self-assembly of active core corona particles into highly ordered and self-healing structures

“…One should note that the mixed state shown in Figure.1(b) is actually a metastable state of the system, rather than the equilibrium state with the lowest free energy. The equilibrium phase diagram in terms of k s (see methods in ref [28][29][30]…”