Surface Wettability-Switchable Janus Fiber Fragments Stabilize Pickering Emulsions for Effective Oil/Water Separation

Abstract

Pickering emulsions indicate stronger resistance against droplet coalescence than the surfactant-stabilized emulsions. To resemble the surfactant amphiphilicity, Janus fiber fragments (JFs) were herein prepared through side-by-side electrospinning of poly(styrene-maleic anhydride) (PSMA) derivatives and cryosection of the aligned fibers, followed by conjugation of hydrophobic cetylamine (C 16 ) and hydrophilic poly(N-isopropylacrylamide) (PNIPAm) ligands on the separate sides. Orthogonal analysis table L 25 (5 6 ) was designed to examine the effect of process parameters on the emulsification efficiency and stability index of Pickering emulsions. The emulsification efficiency is dominated by the JF concentration and length, while the emulsion stability could be prolonged through adjusting the JF concentration and hydrophilic graft density. JF-stabilized emulsions exhibit a much higher stability index (96.4%) than that of Janus microparticle counterparts (37.7%). Though there is no apparent effect on the surface wettability, JFs with PNIPAm grafts of about 2200 Da achieve the most stable Pickering emulsions. Superparamagnetic Fe 3 O 4 nanoparticles are inoculated into JFs to collect emulsion droplets under a magnetic field, and the emulsions could be demulsified at an elevated temperature to harvest oil. Meanwhile, the recovered JF emulsifiers could be repeatedly used without loss of the emulsification efficiency. Thus, this study demonstrates surface-switchable JFs to be effective stabilizers of Pickering emulsions and readily recycled for oil harvesting from wastewater.

Multiresponsive Behavior of the Pickering Emulsifier and Its Application for Collecting Small Oil Droplets in Water

“…Pickering emulsions are stabilized using nanoparticles instead of surfactants, which offer great merits such as environmental friendliness, ease of surface functionalization, and lower toxicity . Thus, Pickering emulsions have been applied to oil spill remediation and oil–water separation. , Stabilization of Pickering emulsions is an important factor for oil–water separation, which is due to nanoparticles adsorbing onto the water–oil interface and encapsulating oil droplets . Additionally, the controlled emulsification and breaking of responsive Pickering emulsions are a great advantage in the process of oil–water separation .…”