Magnetic response emulsions, with regulated motion of droplets by magnetic fields, provide opportunities in system design. Research in Janus emulsion is blooming attributed to excellent multiple chambers, diverse interfaces, and advanced structures. Responsive Janus emulsions are prepared, using two immiscible oils of dimethyl phthalate (DMP)/vegetable oil (VO) and small molecules of magneto-surfactants ([H-G-C 16 ]FeCl 4 ) as stabilizer, in batch-scale by traditional vortex mixing. The composition of emulsion, the concentration of surfactant, and the emulsification energy are applied to control the topology of the structured fluid, and more importantly achieve the quantitative regulation of magnetic response. Janus droplets with clear inner interfaces are successfully constructed solely by magneto-surfactant, and the strategy is universal and even extended to Cerberus emulsions composed of three separated compartments . The magnetic response is visualized by directed moving against gravity and saturated magnetization. The responsivity is enhanced about 44.5%-54.5% accompany with VO lobe transformation from “waxing crescent” to “full moon with a hole”. The magnetic response is increased as high as 80.0% by decreasing the droplet size. Delicate calculations reveal that the ordered arrangement of [H-G-C 16 ]FeCl 4 at the interfaces, mainly contributes to the magnetic response compared with aggregates in the continuous phase. The adsorption on the VO/aq interface dominates the overall response due to the higher affinity of the surfactant to the VO phase. The findings open an avenue in the production of magneto-responsive multiple emulsions , which would push forward future application in smart microreactors, intelligent fluids, and responsive delivery systems.
A magnetic surfactant, which combines the properties of a surfactant with magnetic responsiveness, shows great potential in biotechnology, separation, adsorption, and catalysis, especially in non-invasive manipulation through a magnetic field. However, a molecularly magnetic surfactant is usually paramagnetic for the amorphous and less ordered structures. In this work, magnetic surfactant 1-methyl-3-hexadecane-imidazolium [MnCl2Br] (C16M[Mn]) is reported to self-assemble in water. The C16M[Mn] magnetic surfactant self-assembles in water to form a lamellar hydrogel from 10 to 50 wt % at and below room temperature. The hydrogel changes from a gel to a sol at 30 °C, and the hexadecane chains in the hydrogel change from noncrystalline to crystalline at 0 °C. In the hydrogel state, the lamellar domain spacing is varied from 36 to 45 nm depending on the concentration and self-assembly temperature. After self-assembly, the magnetic susceptibility of the freeze-dried magnetic surfactant is increased. Most important is the fact that the freeze-dried sample at a high concentration (40–50 wt %) shows the highest magnetic susceptibility, which is related to the closer molecular packing and the more ordered structures. The self-assembly-induced increase in magnetic susceptibility provides a method for improving the magnetic properties of a magnetic surfactant.
Two polymerizable surfactants with different numbers of double bonds, 3-undecylene-1-vinylimidazolium bromide (C11VIMBr) and 3-dodecyl-1-vinylimidazolium bromide (C12VIMBr), were chosen to prepare magnetic surfactant monomers by introducing Mn2+, Gd3+ and Ho3+. All the surfactant monomers exhibited paramagnetism except for C12VIMMn that exhibited ferromagnetism. The surface activity results indicated that the magnetic counterions tended to reduce the critical micelle concentration (cmc) and increase the dissociation constant of the surfactants, which was attributed to the stronger hydrophobicity of the magnetic anions than that of Br−. Compared with the surfactant monomers with Br− as counterions, these magnetic surfmers showed thermotropic liquid crystal (LC) behaviors within a certain range of temperature. C11VIMMn, C12VIMMn and C12VIMHo could form smectic A (SmA) LC phases whereas C11VIMGd, C11VIMHo and C12VIMGd produced cubic phases with higher viscosity. The magnetic LC films with ordered nanostructures were directly obtained by in situ polymerization of the magnetic surfmers without a significant change of magnetic strength. The magnetic LC films obtained could be attracted and removed by an external magnet, providing a possibility for the development of magnetically responsive solid electrolytes and efficient adsorbents.
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