W/CO2 microemulsions formed under moderate conditions

Water-in-CO2 microemulsions (W/CO2 MEs) are composed of a dense CO2 (liquid or supercritical CO2) continuous medium and dispersed water droplets stabilized by CO2-philic surfactants. Fluorocarbon (FC) chains were thought to be essential components of CO2-philic surfactants. However, many FCs are non-biodegradable environmental pollutants, toxic to life, bioaccumulative and expensive. Recently, we succeeded to form W/CO2 MEs with the tailor-made double trimethylsilyl (TMS)-alkyl-tail nonionic surfactant and a trace level of a short FC-tail surfactant as a cosurfactant: this system was stable at an easily accessible pressure of 55 bar and temperature of 15 ºC (RB2410068). This new experiment will explore formation of high water-content W/CO2 MEs at moderate P-T conditions with optimized FC-free surfactant structures and compositions. Such easily-accessible and green W/CO2 MEs could offer important practical benefits in terms of safety, low cost, and ease of processing.