In situ small angle neutron scattering study of benzene adsorption in the porous SiO2 glass CPG-10-75

Interactions of benzene with the controlled-pore SiO2 glass CPG-10-75 at 36°C were studied under near contrast matching conditions by use of an in situ small angle neutron scattering technique. SANS data were measured for a range of relative benzene pressures P/Ps under equilibrium and non-equilibrium conditions. The internal surface of dry CPG-10-75 is fractally rough with a fractal dimension Ds=2.30±0.01. After adsorption of a benzene film at P/Ps=0.74, Ds=2.02±0.02, which reveals a smooth liquid/vapor interface. SANS from adsorbed films may serve as a rigorous test of surface roughness. Benzene condensed within the pores upon a sudden increase in P/Ps from 0.74 to 0.84, in fair agreement with the prediction of the Kelvin equation for open-ended cylindrical pores with a nominal diameter of 77 إ.