Surface tension of ethanol in supercritical CO2

Laser interferometric microscopy, applied in this work, enabled simultaneous measurements of the droplet surface tension, σ, and the surface solvent composition. The data, obtained within the temperature interval 313.15–363.15 K and pressure range 60–135 bar, indicated a significantly lower dynamic surface tension compared to the equilibrium. The apparent mixture critical pressures (mcps), determined by zero-σ extrapolation of the equilibrium isotherms, were in an agreement with the theoretical predictions obtained from the Peng-Robinson EOS. A quantitative description of σ based on parachor method indicated the best fit scaling exponent ranging from 3.3 to 3.98 for different temperatures, with mean absolute deviations ±3%. The concentration gradient of ethanol in the droplet diffusion boundary layer accounted for the variation of σ and apparent mcp in the non-equilibrium case.