Vesselin N. Paunov1, Amro Dyab1, Benjamin Holt1, Hartmut Wege1, Olivier Cayre1, Grahame MacKenzie1, Fiona Meldrum2, Simeon Stoyanov3, and Orlin D. Velev4. (1) The University of Hull, Hull, United Kingdom, (2) University of Bristol, Bristol, United Kingdom, (3) Unilever Research, Vlaardingen, Netherlands, (4) North Carolina State University, Raleigh, NC
Novel methods for fabrication of dipolar Janus particles has been proposed based on polymerization of oil-in-water emulsions stabilized with a mixture of water-insoluble cationic and anionic surfactants. An emulsion of polymerizable oil in water was polarized in DC electric field and polymerized while the surfactant monolayer on the emulsion drops is segregated. This “freezes” the dipolar surface charge distribution and produces a suspension of polymer microparticles of permanent electric dipolar moment. Our results show that the produced polymer microparticles retain their polarization when the electric field is switched off for at least several months. The use of this method has been extended to magnetic Janus particles. We also extended this technique for fabrication of anisotropic articles of non-spherical shape based on oil-in-water emulsion templates embedded in a gelled aqueous phase. The gelled emulsion was stretched or compressed macroscopically inducing a local deformation of the emulsion drops. After UV-polymerization of the oil phase, non-spherical anisotropic microparticles of various aspect ratios have been produced. The effect of different macroscopic deformation ratios on the particle shapes has been studied using optical and electron microscopy techniques. Possible applications include photonic crystals with novel symmetries, colloidal substitutes for liquid crystals and water-based electrorheological fluids. We describe here a novel, scaled-down “papier mache” approach to the synthesis of anisotopic microcapsules, in which nano-cotton fibres and polyelectrolytes are used to template calcium carbonate microcrystals with needle-like and rhombohedral morphologies. This technique provides a unique route to producing anisotropic capsules whose morphologies perfectly mirror the shape and size of the template. Further, we demonstrate that this can be achieved through deposition of a single composite layer of nano-cotton fibres and an oppositely charged polyelectrolyte on the chosen template. We also present a simple technique for filling of sporopollenin microcapsules with nanoparticles and insoluble salts by using a chemical reaction or a precipitation process that generates the encapsulated compounds inside the sporopollenin shell. We demonstrate the method by producing magnetic sporopollenin (loaded with magnetite nanoparticles), and sporopollenin filled with calcuim phosphate and organic salts of low solubility.

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