Directing Colloidal Assembly via Selective Depletion

The ability to synthesize and assemble matter on the colloidal scale has recently been at the forefront of research in materials science and nanotechnology. In particular, the ability to direct the assembly of colloids in a directional manner presents a challenge, as many methods of assembly are inherently nonselective. In this work, colloids are synthesized via an emulsion-based method and depletants are made to selectively adsorb onto colloidal surfaces to direct assembly, thus allowing for depletion to only occur under certain conditions. We are able to achieve selective assembly by introducing polymers, changing the pH, and tuning the nature of the depletant. We demonstrate selective assembly by selectively forming single or mixed crystals from a bidispersed suspension of particles by modifying the environment that the colloids are suspended in. We further demonstrate degree of selectivity of the depletion interaction in our colloidal systems by directing the patch-to-patch assembly of Janus colloids into complex structures. Selective depletion offers a new tool to direct assembly in colloidal systems and has the potential to be used to direct the hierarchical assembly of building blocks such as patchy particles and Janus colloids towards desired complex structures.