Molecular dynamics simulation of self-assembly structure for AOK based reverse micelle in supercritical CO2

Molecular dynamics simulations were performed to investigate the structural properties of aqueous reverse micelles of AOK (aerosol-octyl-ketone), a non-fluorinated hydrocarbon surfactant with two symmetrical carbonyl groups in the tail, in supercritical CO2 fluid. The result for the first time demonstrates the atomic-level structural picture for the formation of nanodomain in water-in-CO2 microemulsion based on the AOK surfactant, which is in good agreement with the recent experiment. The dynamics process shows that the self-assembly of the reverse micelle takes a relatively short period of time (∼4 ns) and remains stable over 50 ns. For comparison, the simulation for the AOK/scCO2 system has also been performed and an irregular and sparse reverse micelle structure can be formed in the absence of water molecules. The radial density profiles, the pair radial distribution functions and the orientation distribution have been calculated to investigate the interfacial structure properties. The carbonyl groups in the surfactant tails may enhance the solvation of the AOK surfactant, thereby affording to stabilize the reverse micelle.