Photoresponsive surfactants for controllable and reversible emulsion systems

Surfactants play a crucial role in applications such as oil-water separation, foam flotation , drug delivery, emulsion polymerization , and emulsifier recovery. Stimulus-responsive surfactants, as innovative smart materials, can reversibly control emulsion decomposition or phase transformation, facilitating emulsion circulation and component recovery. In this paper, two short-chain fluoroazobenzene photoresponsive surfactants ( FADC-2 and FADC-4 ) were synthesized. Three different reversible emulsion systems were constructed, leveraging the excellent chemical stability and rapid photoresponse of azobenzene and the trifluoromethyl group as a hydrophobic moiety. The results indicate that under different light exposures, the FADC-2 /n-hexane/water and FADC-4 /n-hexane/water emulsions exhibit reversible emulsification and demulsification cycles, while the FADC-4 /n-octanol/water emulsions show reversible phase transfer. These findings highlight the effectiveness of photoresponsive surfactants in controlled emulsion systems, offering promising applications in fields requiring precise emulsion manipulation and liquid-liquid phase transfer, at the same time advancing the development of environmentally friendly, practical, durable, and stimulus-responsive surfactants.