(6ip) Colloids with Valence: Design, Fabrication, and Directed Self-Assembly

Self-assembly of colloidal particles has emerged as a promising strategy to construct micrometer-scale three-dimensional ordered composite materials such as photonic crystals. Meanwhile, colloidal particles can serve as model building blocks to study the self-assembling processes of molecular systems. However, the lack of directional interactions between isotropic particles has imposed much limitation on the study of colloidal self-assembly. We design new colloidal particles, colloids with valence, which possess reversible, specific, and directional interactions with well-defined symmetries. The primary hypothesis is that particles exhibiting distinct surface patches can be fabricated (patchy particles). The patches can be functionalized with biological or synthetic macromolecules containing recognition units, and provide directional bonding interactions in particle self-assembly.

Based on this hypothesis, we show that patchy particles are synthesized by partially encapsulating small clusters of colloidal microspheres, leading to tailored patch size, geometries, and surface functionalities. Particles with amidinated patches are further functionalized with biotin molecules, to which DNA with single-stranded “sticky ends” are attached. Directed assembly of DNA patchy particles is demonstrated, by which a wide variety of colloidal structures mimicking molecular symmetries are formed. In addition, self-assembly of patchy colloids is viewed as chemical reactions and its kinetics has been studied. The assembling process follows a stepwise-sequential mechanism, as can be described by a model based on diffusion controlled reactions. Apart from using biological molecules and DNA hybridization, a synthetic tri-block copolymer bearing supramolecular recognition moieties are synthesized and functionalized onto carboxyl patchy particles. These surface-modified patchy colloids spontaneously form larger structures such as daisy chains induced by palladated-pincer-pyridine metal coordination. Due to the valence characteristics, patchy colloids introduced will open great opportunities to build a spectacular spectrum of functional materials as well as to study self-assembling processes in more complicated molecular and biological systems.