Surface tension and viscosity of carbon dioxide near the critical point using molecular dynamics simulations and surface light scattering

The present study investigates the surface tension and viscosity of carbon dioxide (CO 2 ) in the vicinity of the critical point using molecular dynamics (MD) simulations and surface light scattering (SLS). The latter technique was applied to simultaneously obtain the sum of the dynamic shear viscosities of the liquid phase, η L , and vapor phase, η V , as well as the surface tension σ at macroscopic thermodynamic equilibrium at temperatures T from (283.15 to 303.65) K, corresponding to reduced temperatures T R from 0.931 to 0.998. The measurement results for ( η L + η V ) and σ with average expanded ( k = 2) uncertainties of (2.4 and 2.6) % agree very well with the few data available in the literature. The T -dependent behavior of the SLS results for σ can be described by a van der Waals-type surface tension equation in accordance with scaling theory. The experimental results for σ of CO 2 served to evaluate the performance of equilibrium molecular dynamics (EMD) simulations in predicting its surface tension together with the phase behavior at T between (288.15 and 298.15) K. For this purpose, seven different force fields (FFs) employed from literature were applied, which provide all-atom or united-atom representations and involve rigid or flexible intramolecular potentials. It was found that a reliable representation of the vapor and liquid densities, vapor pressure, and σ near the critical point can only be realized using rigid FFs, all of which were not optimized against surface tension data.