Smart Amphiphilic Janus Microparticles: One-Step Synthesis and Self-Assembly.

Self-assembly is the process to form ordered compound structures. Theories and experiments involving nanosized Janus particles have proved that the assembled cluster structures are related to the unit number. Micrometer-sized amphiphilic Janus particles could also act as surfactants to stabilize droplets and aggregate to form clusters. When the scale order increases to the millimeter size, particles are usually connected under shape-match mechanism, which means that the assembled structure is related to the particular particle morphology rather than the particle number. Similar to millimeter-sized particles, sub-millimeter-sized particles are larger and heavier such that their gravity cannot be ignored, whereas their Brownian motion could be neglected. To investigate the self-assembly behavior of sub-millimeter-sized Janus particles, we synthesize smart amphiphilic Janus microparticles directly from water-oil Janus droplets in one step by using a double-core capillary device. We find that the amphiphilic Janus particles could also be distributed directionally between the sides of the water-oil interface. When in oil solutions with several water droplets, the particles self-assemble into micelle-like structures to cover the water droplets with the hydrophilic phase inside. After evaporation, structures with a hydrophilic concave and a hydrophobic convex are formed. This paper demonstrates that sub-millimeter-sized amphiphilic Janus particles exhibit similar ability to nano-sized Janus particles to aggregate into clusters with ordered structures.