Droplet Liquid/Liquid Interfaces Generated in a Microfluidic Device for Assembling Janus Inorganic Nanohybrids
Résumé
One among other remarkable methods to produce multifunctional assemblies with different spatial organizations is the use of liquid–liquid (L–L) interfaces. Herein, a droplet microfluidic-based method is reported as a strategy for the assembly of asymmetrical inorganic nanohybrid structures. As a proof of concept and motivated by their wide applications in different fields, we studied the assembly of two building nanoblocks, which are fluorescent silica (160 nm diameter) and gold nanoparticles (15 nm diameter). In this strategy, droplets of an aqueous solution of citrated gold nanoparticles are generated in a continuous flow of amine functionalized fluorescent silica nanoparticles dispersed in cyclohexane using the microdevice. The electrostatic attraction between the two nanoparticles confined at the water/cyclohexane interface to form a Pickering emulsion allowed their assembly. We show that Janus nanohybrids can only be observed when the residence time in the microdevice was less than 30 min, thus avoiding the formation of solid shells for longer residence times. Transmission and scanning electron microscopies, optical microscopies, and UV–vis spectroscopy were used to characterize the resulting assemblies. The results were compared to experiments in bulk which showed that microfluidics offers a higher control over the assembly and reduces the time for their elaboration. Moreover, an analytical model based on transport of nanoparticles and their adsorption onto interfaces is used to rationalize our observations. Both flow recirculation inside and outside the droplets in the microchannel and the confinement effect seem to be relevant for the enhanced nanoparticle transport to the interfaces.