Preparation of poly(N-isopropylacrylamide) hydrogel beads by sedimentation polymerization combined with electrostatic atomization

The preparation of monodisperse, millimeter- or submillimeter-sized polymeric hydrogel beads by a novel production method combining sedimentation polymerization and electrostatic atomization is presented herein. The beads were prepared by drop-wise addition or spray of a pre-gel aqueous solution into silicone oil through a nozzle with application of high voltage, and subsequent free-radical polymerization of the pre-gel droplets during their descent. The thermosensitive poly( N-isopropylacrylamide) hydrogel that was used as the model hydrogel has attracted much attention for application in reaction and separation processes. The size of the pre-gel droplets dispensed from the tip of the nozzle corresponded to the size of the resultant hydrogel beads and was controlled by adjusting the applied voltage. The diameter of the pre-gel droplet was estimated from the equilibrium of forces caused by gravity, the electrostatic force, and the liquid-gas surface tension.