Self-Assembly of Doublets from Flattened Polymer Colloids

Bottom-up fabrication methods are used to assemble strong yet flexible colloidal doublets. Part of a spherical particle is flattened, increasing the effective interaction area with another particle having a flat region. In the presence of a moderate ionic strength, the flat region on one particle will preferentially “bond” to a flat region on another particle in a deep (≥10 <i>kT</i>) secondary energy minimum. No external field is applied during the assembly process. Under the right conditions, the flat–flat bonding strength is ≥10× that of a sphere–sphere interaction. Not only can flat–flat bonds be quite strong, but they are expected to remain freely rotatable and flexible, with negligible energy barriers for rotation because particles reside in a deep secondary energy minimum with a ∼20–30 nm layer of fluid between the ∼1 μm radius particles. We present a controlled technique to flatten the particles at room temperature, the modeling of the interparticle forces for flattened spheres, and the experimental data for the self-assembly of flat–flat doublets.