Molecular dynamics simulations on the dynamics of two-dimensional rounded squares

Abstract

The collective motion of rounded squares with different corner-roundness ζ is studied by molecular dynamics (MD) simulation in this work. Three types of translational collective motion pattern are observed, including gliding, hopping and a mixture of gliding and hopping. Quantitatively, the dynamics of each observed ordered phase is characterized by both mean square displacement and van Hove functions for both translation and rotation. The effect of corner-roundness on the dynamics is further studied by comparing the dynamics of the rhombic crystal phases formed by different corner-rounded particles at a same surface fraction. The results show that as ζ increases from 0.286 to 0.667, the translational collective motion of particles changes from a gliding-dominant pattern to a hopping-dominant pattern, whereas the rotational motion pattern is hopping-like and does not change in its type, but the rotational hopping becomes much more frequent as ζ increases (i.e., as particles become more rounded). A simple geometrical model is proposed to explain the trend of gliding motion observed in MD simulations.

The cooperative migration dynamics of particles correlates to the nature of hexatic–isotropic phase transition in 2D systems of corner-rounded hexagons

“…Taken all these results together, it seems to suggest that it is this cooperative effort of many particles within a certain local region that contributes to the observed different migrating clusters. Similar cooperative effect has also been reported in earlier studies [ 5 , 40 ]. For example, a previous study has shown that the occurrence of hopping is often with the help of transient defects under the density fluctuations around the hopping particle and its neighbors [5] .…”

“…Phase behavior of two-dimensional (2D) colloidal systems, due to its significance in both fundamental research and technological applications, has received lots of attention. Extensive studies including both simulations [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] and experiments [ 9 , 10 ] have been reported in the past several decades. However, to fully understand the relationship between specific phase behavior and particle properties is still a challenge because the richness of emergent phase behavior makes it difficult to develop a general framework to unify all the phase behavior that we have observed [ 1 , [9] , [10] , [11] , [12] ].…”

“…However, to fully understand the relationship between specific phase behavior and particle properties is still a challenge because the richness of emergent phase behavior makes it difficult to develop a general framework to unify all the phase behavior that we have observed [ 1 , [9] , [10] , [11] , [12] ]. It has been demonstrated that different phases can exhibit different particle dynamics such as hopping [ 13 , 14 ], gliding [ 5 , 15 ] or string-like [16] motions observed in 2D crystal phases and string-like cooperative motion in three-dimensional (3D) glass-forming liquids [17] , [18] , [19] , [20] . Thus, dynamics measurements in colloidal systems not only depict the motion feature of single particles, but also provide a way to understand the phase behavior of colloids via kinetic information [ 5 , 15 , [21] , [22] , [23] ].…”

“…It has been demonstrated that different phases can exhibit different particle dynamics such as hopping [ 13 , 14 ], gliding [ 5 , 15 ] or string-like [16] motions observed in 2D crystal phases and string-like cooperative motion in three-dimensional (3D) glass-forming liquids [17] , [18] , [19] , [20] . Thus, dynamics measurements in colloidal systems not only depict the motion feature of single particles, but also provide a way to understand the phase behavior of colloids via kinetic information [ 5 , 15 , [21] , [22] , [23] ].…”

Active Anisotropic Colloids from Colloidal Monolayers

“…Upon increasing the shape parameter of Cubic-lattice Λ 0 -lattice Λ 1 -lattice the superballs, however, the ratio of the fraction of the particles being packed into the Λ 1 -lattice to the Λ 0 -lattice was observed to increase as a result of the Λ 1 -lattice becoming increasingly more dense upon an increase in the shape parameter. The phase behaviour observed in these experiments agree with those found in Monte Carlo simulations [66]. The horizontal and vertical deposition method allows the formation of relatively large and cm-sized lattices.…”