Soft Potential for the Self-Assembly of Colloidal Clusters and Spheres, Structures and Photonic Band Gaps

We recently demonstrated experimentally and in simulations that DNA coated tetrahedral clusters and spheres self-assemble into a colloidal analog of the MgCu₂ structure[1], interpenetrated diamond and pyrochlore lattices. For very short range attractive potential between building blocks, the desired superstructure only forms when clusters are partially compressed. Under those conditions, merging particles in the cluster is necessary to fill the gap between the two sublattices, increase the number of contacts between complementary particles and stabilize the final assembly.
Here we explore the domain of formation of the MgCu₂ structure as the softness and the reach of the attractive potential are increased. We show that the domain of existence of this Laves phase grows significantly for softer potentials. Experimentally, a softer potential could be achieved by using a longer polymer brush to coat the particles, starting from microgels, or simply by reducing the size of the hard cores. We will finally discuss the photonic band structure and the gap properties of the formed sublattices.
[1] Ducrot et al., Nat. Mat. 2017 16, 652