Peculiarities of the capillary condensation of carbon dioxide in the vicinity of the critical point

Experimental data on the small-angle diffuse transmittance of a CO2-saturated porous layer (a filter paper) are presented depending on the pressure in the vicinity (below and above) of the critical point. It is found that the increase in the diffuse transmittance of the studied system at an isothermally increasing pressure point up to the saturation vapor pressure below the critical point is governed by capillary condensation of carbon dioxide in mesopores with the characteristic size of 50–100 nm. In this case the volume fraction of the condensed liquid phase at a given pressure is determined by the effective surface energy of the liquid-gas interface, which is proportional to the first derivative of the surface tension with respect to temperature. The obtained results can be considered as a basis for refractometric densitometry of near-critical liquids and supercritical (SC) fluids in optically dense disperse systems.