Quantum Chemical Study of the Carbon Dioxide-Philicity of Surfactants: Effects of Tail Functionalization

Abstract

Carbon dioxide (CO 2 )-philic surfactants have broad application prospects in organic synthesis, fracture-enhanced oil recovery, polymerization, extraction, and other fields and can be used to enhance the viscosity of supercritical CO 2 (scCO 2 ). In this work, the relationship between the functional group of the surfactant tail and CO 2 -philicity is studied from a new perspective using density functional theory. Three common functional group types (fluorinated, oxidative, and methyl groups) were investigated. The analysis of binding energy demonstrates that all three types of functional groups can improve the CO 2 -philicity of the surfactant. Among these three kinds of functional groups, the strongest interaction with CO 2 molecules is observed for oxidative functional groups followed by semifluorinated, fluorinated, and methyl groups. However, the CO 2 molecules tend to be adsorbed onto the middle segment of the oxidative group, and the intrusion of the CO 2 molecules results in the low solubility of oxidative surfactants. In contrast, fluorinated and methyl groups interact with CO 2 at the end of the surfactant tail. As a result, the fluorinated surfactants show the best solubility in CO 2 . Therefore, the solubility of a surfactant in CO 2 is not only related to the interaction strength between the surfactant and CO 2 , it also depends on the interaction structure. The results of this study provide a new strategy for evaluating surfactant CO 2 -philicity and provide guidance for the design of surfactants with high solubility in scCO 2 .

Steric effects stabilize reverse micelle domains in supercritical CO2 by determined conformation: restrictions of water and cations

“…Ultimately, the steric effect arising from these interactions leads to the development of CO 2 -philic behavior in the surfactant. In addition, previous studies using quantum chemical methods have shown that 81 fluorine with a high negative charge (−0.26, different from hydrogen's 0.09) could be forming a coordination interaction similar to water molecules and play a role similar to hydrogen bonding to cause CO 2 -philicity. Studies have shown that these interactions binding conformation of surfactants were weaker than bond intramolecular interactions but stronger than normal non-bonding intermolecular interactions.…”