Preparation of polymeric Janus microparticles with hierarchically porous structure and enhanced anisotropy.

Anisotropic Janus particles are of great interest for many applications. It is well known that behavior and utility of Janus particles are highly dependent on their chemistry and geometry. Herein, we report the synthesis of monodisperse polymeric Janus microparticles that were anisotropic not only in chemistry and shape but also in surface morphology and porosity, via a modified seeded polymerization technique. Chemical composition, shape, morphology and porosity of the polymeric Janus microparticles were flexibly controlled by utilizing different quantities and species of monomer and porogen. The polymeric Janus microparticles exhibited hierarchically porous structure, including micro- and meso-pores as evidenced by isothermal nitrogen adsorption and desorption. Due to the high specific surface area, anisotropy of the polymeric Janus microparticles was enhanced according to the greater fluorescence contrast on distinct sides of the polymeric Janus microparticles. Moreover, swelling and phase-separation processes of cross-linked seeds were in situ observed on an optical microscope to demonstrate the formation mechanism of the polymeric Janus microparticles.