Study on the Thickening Behavior and Mechanism of Supercritical CO ₂ by Modified Polysiloxane

Abstract

Supercritical CO₂ has been widely concerned because of its clean environmental protection and excellent performance. However, the low viscosity limits its wide application. To this issue, researchers usually use thickeners to improve its viscosity and siloxane-type polymer is regarded as clean and cheap thickeners. In this work, by comparing the thickening properties of vinyl polysiloxane, hydroxyl polysiloxane and polydimethylsiloxane, the potential thickeners of supercritical CO₂ is screened. The results show that vinyl polysiloxane has the best thickening performance. The dissolution and thickening behavior of vinyl polysiloxane are further studied. The results show that with the increase of kinematic viscosity and concentration, the dissolution pressure and thickening capacity of vinyl polysiloxanein in supercritical CO₂ increase. At the experimental conditions, the maximum viscosity of supercritical CO₂ can be increased to 14.87 mPa·s. In addition, the dissolution pressure of vinyl polysiloxane in supercritical CO₂ decreases with the increase of cosolvent concentration, while the viscosity slightly decreases. Finally, the thickening mechanism of these thickeners was studied by molecular dynamics simulation. The role of functional groups in the dissolution and thickening of CO₂ is discussed. It can provide theoretical support for the synthesis and screening of CO₂ thickeners in the future.

Keywords: Supercritical CO2, Vinyl Polysiloxane, Thickening Behavior, Molecular Dynamics Simulation, Thickening Mechanism