Synthesis of polyacrylamide (PAM) beads in microreactors

Abstract

A microreactor based continuous inverse suspension polymerization method for synthesis of uniform spherical polyacrylamide (PAM) hydrogel beads is reported. Aqueous phase containing monomer, cross-linker and initiator was dispersed in the form of droplets into a carrier phase (dodecane) by using a microfluidic T-junction. The residence time for the reaction was provided by a microbore tube connected to the T-junction. The effects of factors such as O/A ratio (ratio of the volumetric flow rates of the organic carrier phase and the aqueous phase), microbore tube diameter, design of the microfluidic junction and monomer concentration on the shape, size and uniformity of the beads formed were studied in detail. Two different mixing approaches – in-situ mixing and ex-situ mixing – were also compared. The size of the beads could be varied by changing the O/A ratio. The design of the microfluidic junction and the diameter of the residence time element were found to have significant effect on the size and shape of the beads. Spherical and monodispersed (polydispersity index < 10 %) PAM hydrogel beads could be synthesized by using the microreactor comprising 800 μm diameter microfluidic T-junction as the dispersing device followed by a microbore tube serving as the residence time element.