Engineering porous two-dimensional lattices via self-assembly of non-convex hexagonal platelets

Abstract

In this work, a molecular-dynamics simulation study of the formation of ordered two-dimensional porous structures is presented. The structures are formed by the self-assembly of non-convex hexagonal platelets confined in a plane. By designing the interparticle interaction, a variety of structures are observed. For purely repulsive particles, the system forms a striped crystalline structure with the pmg symmetry group, which also corresponds to its close-packed structure. As the attractive interactions between the edges are turned on, the edges of close neighbours start to align (pair), but due to the non-convex shape of the platelets, only three out of six edges can be paired although there is no preference as to which particular three edges these might be. This geometric constraint promotes the formation of an unusual porous hexagonal phase with a long-range translational order but a short-range offset rotational displacement disorder in which three types of regular and irregular hexagonal pores are formed. The formation of the three hexagonal pore shapes is due to the energetic degeneracy of the three configurations. Finally, we show that when the attractive non-convex hexagonal platelets are functionalized with oligomeric chains tethered to the three main vertices of the particles, a porous hexagonal phase with the p6(632) symmetry is formed in which chiral symmetry breaking is observed despite the particles being achiral. As this functionalized platelet model does not favour one enantiomer over the other, grains with different chiral symmetries are formed, but eventually when an imbalance of the enantiomeric population takes place, a single chiral structure is formed in a similar way to that in the Viedma ripening effect.