77. Hemingway, Melinda G.; Gupta, Ram B.; Elton, David J.  Hydrogel Nanopowder Production by Inverse-Miniemulsion Polymerization and Supercritical Drying.    Industrial & Engineering Chemistry Research  (2010),  49(20),  10094-10099.   


Hydrogel nanoparticles can be successfully produced by polymn. in inverse miniemulsions, for use in a variety of applications including diagnosis, drug delivery, sepn., 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 supercrit. CO2 drying to obtain free-flowing hydrogel nanoparticles.  Polyacrylamide hydrogel nanoparticles (.apprx.100 nm in diam.) are produced in an inverse miniemulsion composed of a cyclohexane continuous phase, a water dispersed phase, and a nonionic surfactant.  The polymd. miniemulsion is dried by injection into supercrit. CO2 which results in rapid removal of cyclohexane, water, and surfactant.  The morphol., particle size, and size distribution of the nanoparticles are detd. using dynamic light scattering and SEM.  The proposed miniemulsion polymn. supercrit. drying (MPSD) method produces a hydrogel nanopowder with much lower agglomeration or residual surfactant as compared to convention drying.  In addn., the MPSD method produced solvent-free nanoparticles due to efficient extraction by supercritical CO2.     


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