LAUSR

The sizes and shapes of polymer particles determine their performance and application. In this paper, ethyl cellulose particles with different morphologies are generated through extraction and solidification in a microfluidic device with double T-junctions. Droplets of ethyl acetate containing ethyl cellulose are formed first, then, pure water is employed to extract the solvents in the droplets and the ethyl cellulose is solidified to form monodisperse particles. By changing the flow rates of the continuous phase and the dispersed phase and the concentration of ethyl cellulose, red-blood-cell-like, doughnut-like, dimpled and spherical particles are fabricated, and the regime of different particle morphologies is given. The more important is that the physical mechanisms and explanations of the formation of different particle morphologies are clearly disclosed by analyzing the circulation flows outside and inside the droplets. The flow patterns in the microchannel, and the diffusion and solidification properties of the molecules are the key factors that affect the final morphology of particles. Due to the circulation, there are two stagnation points at the front and rear of the droplet, and they are the approximate locations where the dimple in the dimpled particle, the hole in the doughnut-like particle and the two pits in the red-blood-cell-like particles are formed. These analysis and results are useful in flow chemistry, in the fabrication of particle materials, and so on.