Microscopic properties and stabilization mechanism of a supercritical carbon dioxide microemulsion with extremely high water content.

Abstract Hypothesis Developing the supercritical carbon dioxide microemulsion with a broad water content (W0) window can provide more possibility for designing highly efficient chemical processes, which is challenging due to the lack of comprehension about its formation mechanism. Molecular dynamics simulation method is expected to reveal the microscopic stabilization mechanism of high-W0 microemulsions. Simulations All-atom molecular dynamics simulations of the ternary systems with varied W0 stabilized by 4FG(EO)2 surfactant were designed according to phase behavior experiments. A systematic investigation was performed concerning the self-assembling, equilibrium morphology and detailed microstructure of the microemulsion droplet. An in-depth comparative study about the distribution of both H2O and CO2, the interfacial behaviors of 4FG(EO)2, as well as the microscopic interactions was conducted. Findings For the first time, direct evidence was provided for the formation of water-in-carbon dioxide microemulsion with extremely high W0 (80) under the effect of 4FG(EO)2. Furthermore, a unique interfacial phenomenon, i. e. CO2 accumulating at the interface, was revealed to be responsible for the formation and enhanced stability of the nanosized droplet with high W0. This should set a new guiding star for synthesizing and selecting effective interfacial modifiers to create high-W0 microemulsions.