Molecular Dynamics Simulation of the Compatibility Between Supercritical Carbon Dioxide and Coating Resins Assisted by Co-Solvents

The use of supercritical carbon dioxide (ScCO₂) as a replacement for volatile organic solvents in coatings has the potential to reduce air pollution. This paper presents the findings of a molecular dynamics simulation study investigating the dissolution behavior of polyvinylidene fluoride (PVDF) in ScCO₂ assisted by five co-solvents. On the basis of solubility parameters, interaction binding energy, and radial distribution functions, the impacts of temperature, pressure, and co-solvents on the compatibility of ScCO₂ and PVDF were investigated at the microscopic level. The simulation results demonstrated that low-temperature and high-pressure conditions facilitate the dissolution of PVDF in ScCO₂, where the optimal conditions are 308.15 K and 16 MPa. The enhancement of the solubility performance of ScCO₂ slowed down with increasing pressure, but was more sensitive to changes in temperature. The weak attraction between PVDF and ScCO₂ was synergized by van der Waals and electrostatic forces, making it challenging to achieve complete and homogeneous mixing. The use of co-solvents with strong polarity can enhance the solvent system's solubility. Ethanol and 2-butoxy-1-ethanol have obvious solubilizing abilities due to the hydrogen bond donors, which can generate hydrogen bonding interactions with ScCO₂, increase the polarity of the solvent system, and promote the compatibility of ScCO₂ with PVDF.