Dynamic emulsion droplets enabled by interfacial assembly of azobenzene-functionalized nanoparticles under light and magnetic field

Hypothesis The ability to control the assembly of micro/nanosized particles at liquid-liquid interface with external inputs promises new opportunities in nanofabrication and biomedicines. This work aims to demonstrate a way to control of dynamic assembly of nanoparticles at liquid-liquid interface by light and magnetic field, which consequently enables the formation of dynamic emulsion droplets. Experiments Magnetic Fe 3 O 4 nanoparticles functionalized with azobenzene moieties (Fe 3 O 4 @AZO) were synthesized and were dispersed in toluene/(N, N -dimethylformamide, DMF) binary solvent. After irradiation with UV or visible light , the assembly behavior of these Fe 3 O 4 nanoparticles were evaluated by electron microscopy and fluorescent microscopy. Findings Under UV light , Fe 3 O 4 @AZO nanoparticles were self-assembled due to the increase of dipolar interaction from the photoisomerization of azobenzene and polar molecules , DMF, were harvested from a binary solvent of DMF/toluene. While under visible light, a relief of dipolar interactions between Fe 3 O 4 @AZO nanoparticles can induce the secondary assembly of these Fe 3 O 4 @AZO nanoparticles at DMF-toluene interface, resulting in DMF droplets covered by a layer of nanoparticle superlattices . More importantly, coupled with a magnetic field, these emulsion droplets can be shaped into one dimensional ones during the interfacial assembly process, thereby giving rise to dynamic emulsions controlled by light and magnetic field.