Thermomagnetically Responsive γ‐Fe2O3@Wax@SiO2 Sub‐Micrometer Capsules

A three steps synthesis route is proposed to generate thermosensitive and magnetically responsive γ‐Fe₂O₃@Wax@SiO₂ sub‐micrometer capsules with a paraffinic core and a solid and brittle shell. The process integrates Pickering‐based emulsions, inorganic and sol–gel chemistries to promote monodisperse in size wax droplets, γ‐Fe₂O₃ nanoparticles and mineralization of the wax/water interfaces. Hybrid capsules are obtained with an average size around 800 nm, representing the first example of sub‐micrometer capsules generated employing Pickering emulsions as templates. Cetyltrimethylammonium bromide (CTAB) cationic surfactant added during mineralization at concentrations between 0.17 and 1.0 wt% impacts the shell density. The shell density seems to improve its mechanical strength while affording a low wax expansion volume without breaking for CTAB concentrations above 1.0 wt%. At lower CTAB concentration (0.17 wt%), the silica shell becomes less bulky and cannot resist the wax dilatation induced by the solid‐to‐liquid phase transition imposed by hyperthermia. The magnetically induced heating provided by the internal magnetic moments is sufficient to melt the wax core, expanding its volume, inducing thereby the surrounding silica shell rupture. Such γ‐Fe₂O₃@Stearic Acid@Wax@SiO₂ sub‐micrometer capsules allow a sustained wax release with time, whereby 20% of the wax is released after 50 min of alternating magnetic field treatment.