Membrane Emulsification and Solvent Pervaporation Processes for the Continuous Synthesis of Functional Magnetic and Janus Nanobeads

摘要

We discuss the integration of membrane emulsificationnand pervaporation processes for the continuous production ofnfunctional materials, such as silica-encapsulated magnetite nanoparticlenclusters and asymmetric Janus nanoparticles, by the emulsion dropletnsolvent evaporation method, which has traditionally been performed innsmall-scale batch systems. An organic solvent containing primarynmagnetite nanoparticles (∼10 nm) coated with oleic acid was dispersednin a continuous aqueous phase by membrane emulsification, whichnenabled the consistent production of nanoparticle-laden solventndroplets of well-controlled size with narrow size distributions. Thensolvent was removed from the emulsion by pervaporation. Prior toncomplete solvent removal, the nanoparticle packing density within thenclusters was a function of the residence time in the pervaporation unit. The final clusters formed, ∼100−300 nm in size, exhibitednthe same superparamagnetic behavior as the primary nanoparticles, and were stable in aqueous media with a zeta potential of −70nmV at neutral pH. A facile method was used to coat the nanoclusters with a silica shell, providing sites for surfacenfunctionalization with a range of organic ligands. The nanoparticles and clusters were analyzed by a variety of techniques,nincluding TGA, DLS, TEM, EDS, and SQUID. The effects of various parameters, such as the membrane dimensions and flownrate through the unit, on the mass transport rates were elucidated through a parametric modeling study. The applicability of thenmethods to the production of polymeric beads and more complex particles was demonstrated; to create Janus structures, organicnpolymer solutions were dispersed as droplets in continuous aqueous phases, and the solvent was subsequently evaporated. ThenJanus particles consisted either of polymeric cores with magnetite nanoparticles clustered as islands on their surfaces, or of twonphase-separated polymers, each constituting half of any given polymeric particle.