Hydrogel Nanopowder Production by Inverse-Miniemulsion Polymerization and Supercritical Drying

Hydrogel nanoparticles can be successfully produced by polymerization in inverse miniemulsions, for use in a variety of applications including diagnosis, drug delivery, separation, soil stabilization, and absorption. Unfortunately, conventional drying techniques result in agglomerated powder due to the sticky nature of the wet hydrogel particles. This work utilizes supercritical CO2 drying to obtain free-flowing hydrogel nanoparticles. Polyacrylamide hydrogel nanoparticles (similar to 100 nm in diameter) are produced in an inverse miniemulsion composed of a cyclohexane continuous phase, a water dispersed phase, and a nonionic surfactant. The polymerized miniemulsion is dried by injection into supercritical CO2 which results in rapid removal of cyclohexane, water, and surfactant. The morphology, particle size, and size distribution of the nanoparticles are determined using dynamic light scattering and scanning electron microscopy. The proposed miniemulsion polymerization supercritical drying (MPSD) method produces a hydrogel nanopowder with much lower agglomeration or residual surfactant as compared to convention drying. In addition, the MPSD method produced solvent-free nanoparticles due to efficient extraction by supercritical CO2.