Self-assembly Of Bowl-shaped Ploymer Microparticles:Experiment And Computer Simulation

In recent years, the influence of shape on particle self-assembly has intrigued humankind. In this paper, we studied the self-assemblies of bowl-like particle and flattened particle, including the experimental work and computer simulation.In experiment, we proposed a promising method that combined microfluidic technique, solvent evaporation and selective dissolution to prepare uniform concaved particles. 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 concaved particles were obtained through selective dissolution of PMMA domain in the Janus composite particle with acetic acid. Moreover, depletion-induced self-assembly of the prepared concaved particles was investigated, and polymeric work-like chains with head-to-tail configuration were observed.In simulation, rigid body Brownian dynamics method was employed to simulate the self-assembly of concaved and flattened particles where the potential field between particles is quantitatively extracted from the all-atom objects, applying a tabulated and interpolation method. The simulation results show that the particle shapes strongly affects self-assembled structures: for concaved particles, the stable assembled structure is a head-to-end stacking structure; however, for flattened particles, the final structure is a face-to-face stacking structure. The stability of self-assembly structures strongly depend on the extent of concaved and flattened particles and the stacking structures become more stable with the depth of the concaved or flatten parts increasing. To deeply understand the self-assembly kinetics of the self-assembly process, the stable and all metastable conformations are analyzed according to the potential profile of two particles and the transition minimum energy paths(MEPs) from metastable states to the stable state with different active energies are calculated. These results are compared with experiments and an excellent agreement is achieved. This work provides rich information and is valuable to deep understand the self-assembly mechanism of nonspherical particles.