Complex Suspended Janus Droplets Constructed through Solvent Evaporation-Induced Phase Separation at the Air–Liquid Interface

Abstract

Phase separation technology has attracted extensive scientific interest because of its intriguing structure changes during the phase separation process. Phase separation inside emulsion droplets in continuous surroundings has been well studied in recent years. Many investigations have also been conducted to study the droplet phase separation phenomena in noncontinuous surroundings. However, studies on the phase separation phenomena and the spreading behavior of suspended droplets at the air–liquid interface were rarely reported. In this study, PEGDA-glycerol suspended Janus droplets with a patchy structure were produced by utilizing solvent evaporation-induced droplet phase separation at the air–liquid interface. By altering the glycerol/PEGDA volume ratio, the initial proportion of ethanol, and the concentration of surfactants, suspended droplets with different morphologies can be achieved, which include filbert-shaped droplets (FSDs), half lotus seedpod single-phase Janus droplets (HLSDs), lotus seedpod single-phase Janus droplets (LSDs), lotus seedpod-shaped droplets (LSSDs), multiple-bulge droplets (MBDs), and half gourd-shaped droplets (HGSDs). A patchy structure was generated at the air–droplet interface, which was attributed to the Marangoni stresses induced by nonuniform evaporation. Furthermore, a modified spreading coefficient theory was constructed and verified to illustrate the phase separation at the air–droplet interface, which was the first research to predict the phase separation phenomena at the air–liquid interface via spreading coefficients theory. Moreover, we studied the factors that led to the droplets being able to float by designing the combined parameters, including three interfacial tensions and the equilibrium contact angles. Therefore, a simple and versatile strategy for creating suspended Janus droplets has been developed for the first time, which holds significant potential in a variety of applications for material synthesis, such as the electrospinning solution behavior when sprayed from the nozzle into the air.

Janus Hemispheres through Controlled Polymerization-Induced Phase Separations within Wax Droplets

“…Janus particles, especially polymeric Janus particles, are commonly fabricated from controlled phase separation, − self-assembly strategy, ,− seed-mediated emulsion polymerization, − and microfluidic preparation strategy. ,,,− The controlled phase separation within restricted space is extremely promising without doubt due to its versatility. Phase separation is usually induced by polymerization − or/and solvent evaporation. − Most recently, some other strategies, including nonsolvent-induced phase separation, diffusion-induced phase separation, gravity-induced phase separation, and thermal phase separation, − were reported. Indeed, the controlled phase separation has achieved large-scale, controllable, reliable, and simple fabrication of Janus particles.…”