Structure and phase transitions of two-dimensional core-softened colloidal dumbbells: a molecular dynamics study
ZY Yang and M Dutt and YC Chiew, MATERIALS RESEARCH EXPRESS, 6, 075076 (2019).
Formation of two-dimensional (2D) quasi-crystalline structure by colloidal dumbbells interacting via a core-softened potential is studied using molecular dynamics simulations. Owing to the presence of two length scales associated with the rigid bond length of the dumbbell and the minimum of the core-softened repulsive force well, the dumbbell system exhibits rich complex 2D patterns ranging from low-density triangular ordered lattice, coupled stripe-ordered triangular lattice structure, hexagonal lattice, Kagome patterns, to high density clusters as density increases. At very high density, the 2D dumbbells form compact triangular ordered lattice. We have also identified the order- to-disorder transition temperature at which the ordered phase transitions to disordered structure by examining the potential energy, heat capacity and radial distribution functions of the system. In addition to 2D dimeric dumbbells, we studied the structures formed by 2D monomeric spheres that interact through the same core-softened potential. We found that although the monomeric spheres can produce most of the quasi crystalline patterns found for the dumbbell system, there are notable differences. The interplay of the two spatial length scales present in the dumbbells can produce a unique coupled stripe-triangular lattice structure at intermediate densities that is not observed for monomeric particles. The disparity between the two spatial lengths also has the effect of disrupting the formation of regular patterns leading to irregular and defective hexagons and Kagome lattices. This study shows that the two spatial length scales, present in the dumbbells, can be utilized to generate unique structures and demonstrates the potential for using dumbbells as building blocks for creating 2D structures.
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