Complex structures generated by competing interactions in harmonically confined colloidal suspensions.

We investigate the structural properties of colloidal particle systems interacting via an isotropic pair potential and confined by a three-dimensional harmonic potential. The interaction potential has a repulsive-attractive-repulsive profile that varies with the interparticle distance (also known as a 'mermaid' potential). We performed Langevin dynamics simulations to find the equilibrium configurations of the system. We show that particles can self-assemble in complex structural patterns, such as compact disks, fringed disks, rods, spherical clusters with superficial entrances among others. Also, for particular values of the parameters of the interaction potential, we could identify that some configurations were formed by quasi two-dimensional (2D) structures which are stable for 2D systems.

Structural ordering of trapped colloids with competing interactions.

The structure of colloids with competing interactions which are confined in a harmonic external trap potential is analyzed numerically by energy minimization in two spatial dimensions. A wealth of different cluster structures is found to be stable including clusters with a fringed outer rim (reminiscent to an ornamental border), clusters perforated with voids, as well as clusters with a crystalline core and a disordered rim. All cluster structures occur in a two-dimensional parameter space. The structural ordering can therefore be efficiently tuned by changing few parameters only providing access to a controlled fabrication of colloidal clusters.