Magnetic nanoparticles-induced anisotropic shrinkage of polymer emulsion droplets

We here report magnetic nanoparticles (NPs)-induced buckling instability and anisotropic shrinkage behavior of polymer emulsion droplets. The oil-in-water emulsion is stabilized by the surfactant, and NPs are dispersed into the oil phase. The surface ligands (oleic acid and oleylamine) number of the NPs is an important factor to affect the shrinkage process. When a part of the ligands of the NPs is removed, the NPs show good interface attachment at the oil-water interface even with the presence of a large amount of surfactant. The increase of the interfacial viscoelasticity resulting from the attachment of NPs induced the occurrence of a buckling process. The mechanism is explored and the effect of the concentration of polystyrene and NPs is investigated in detail. The results could be helpful to understand and solve problems related with coating techniques and elastic instabilities in nature.