Dissolution Mechanism of Nonionic Polyether Surfactants in Supercritical CO₂

Polyoxyethylene ether is an efficient CO2-philic compound with significant potential applications in CO2 flooding, which requires CO2-philic surfactants with high solubility in supercritical CO2 (scCO2). This study elucidates the molecular and atomic-level dissolution mechanism of the fatty alcohol polyoxyethylene ether (AEO) in scCO2 by combining phase-behavior experiments and molecular dynamics simulations. The solubility of AEO in scCO2 is measured using a semiconductor laser. AEO containing three polyoxyethylene (EO) groups exhibited the highest solubility in scCO2.The solubility of AEO in scCO2 decreased with an increase in the number of EO groups. Molecular dynamics simulations reveal that the interaction force between the AEO and CO2 is predominantly determined by van der Waals forces, which account for 70% of the total interaction force, while the interactions between the alkyl chain, EO group, and CO2 in AEO are primarily driven by Lewis acid–base (LA-LB) interactions and dispersion forces. The strength of these interactions is a key determinant in the dissolution of AEO–CO2, while the structure of AEO facilitates its dissolution in CO2. The number of CO2 binding sites in AEO molecules increases with the free volume fraction and diffusion coefficient, allowing an optimal conformation with superior CO2 affinity owing to greater contact with CO2 molecules. Ethanol interacts with CO2, thereby strengthening the LA-LB interactions and dispersion forces between AEO and CO2 and thus significantly enhancing the solubility of AEO in CO2.