Preparation and assembly of concave polymer microparticlesElectronic supplementary information (ESI) available: Additional plots showing the corresponding size distribution of PS/PMMA and (PVP)PS/PMMA Janus particles were displayed in Fig. S1 and S2. See DOI: 10.1039/c5ra04110d

This report proposed a promising method that combined microfluidic techniques, phase separation and selective dissolution to prepare uniform concave polystyrene (PS) microparticles. Monodisperse emulsion droplets containing PS and poly(methyl methacrylate) (PMMA) in chloroform were firstly obtained using a microcapillary-based microfluidic device. Uniform PS/PMMA Janus composite particles were then generated through the phase separation between PS and PMMA within the emulsion droplets during organic solvent evaporation. Subsequently, uniform PS concave particles were obtained through selective dissolution of the PMMA domain in the Janus composite particle with acetic acid. Moreover, depletion-mediated directional self-assembly of the prepared concave PS particles was investigated, and polymeric worm-like chains with head-to-tail configuration were observed. A promising method that combined microfluidics, solvent evaporation and selective dissolution was proposed to prepare concaved polymer microparticles.