Controllable Preparation of Polyacrylamide Hydrogel Microspheres in a Coaxial Microfluidic Device

A thermal-initiated polymerization procedure is described for the controlled preparation of monodispersed polyacrylamide (PAM) hydrogel microspheres. A coaxial microfluidic device was designed to disperse uniform drops (∼500 μm) of acrylamide monomer aqueous solution into n -octane. Using a delay loop immersed into a heat bath, the polymerization is initiated and carried out in separate droplets. Combining the improvement of heat transfer in the microfluidic device and the sufficient addition of n -octane, the controllable preparation can still be achieved at 95 °C, much higher than 20–60 °C as reported prevalently. Herein, the PAM microspheres can be prepared within 2 min or less, with the CV of diameter less than 4%. Furthermore, based on this controllable reaction platform, PAM microspheres were prepared at various reaction temperatures (higher than 90 °C) and monomer solution compositions to investigate the fundamental rules of controlling on their skeleton structure and absorbent capacity in deionized water.