Magnetically induced demulsification of water and castor oil dispersions stabilized by Fe3O4-coated cellulose nanocrystals

Superparamagnetic iron oxide (Fe3O4) nanoparticle (NP) coated cellulose nanocrystals (CNCs) were synthesized and used to prepare emulsions with magnetically controlled stability. Magnetite NPs were deposited onto the surface of wood pulp CNCs (WCNCs) and bacterial CNCs (BCNCs) by a one-step coprecipitation method. The effect of the CNC to Fe3O4 mass ratio (1:1, 1:2, and 1:4) was varied to optimize the colloidal, magnetic and emulsifying properties of the hybrid NPs. TEM images showed that the 1:4 ratios lead to greater coverage of Fe3O4 than lower Fe3O4 loadings (1:1, and 1:2). The CNCs and Fe3O4 appeared to interact via hydrogen bonding between the hydroxyl groups on the surfaces of both particles. The hybrid NPs had high saturation magnetizations of 56 emu/g for WCNC/Fe3O4 (1:4) and 60 emu/g for BCNC/Fe3O4 (1:4). In addition, they were efficient stabilizers for castor oil and water emulsions. The magnetite lowered the colloidal stability of the CNCs while providing superparamagnetic properties which allowed stabilization of Pickering emulsions and the subsequent depletion of the Pickering effect by an external magnet. Water-in-oil emulsions, with oil contents of 70% and 90% V/V, were broken by an external magnet, while the CNC/ Fe3O4 NPs were recovered and recycled. The 30% and 50% V/V oil emulsions were oil-in-water and could not be broken by the magnet, probably due to higher emulsion stability. The fabricated magnetic CNCs have potential use in magnetically driven separations, drug delivery, and oil recovery