IN-SITU SMALL-ANGLE NEUTRON-SCATTERING STUDY OF BENZENE ADSORPTION INTHE POROUS SIO2 GLASS CPG-10-75

Interactions of benzene with the controlled-pore SiO2, glass CPG-10-75 at 36 degrees C were studied under near contrast matching conditions by use of an in situ small angle neutron scattering technique. SANS da ta were measured for a range of relative benzene pressures P/P-s, unde r equilibrium and non-equilibrium conditions. The internal surface of dry CPG-10-75 is fractally rough with a fractal dimension D-s, = 2.30 +/- 0.01. After adsorption of a benzene film at P/P-s, = 0.74, D-s,= 2 .02 +/-: 0.02, which reveals a smooth liquid/vapor interface. SANS fro m adsorbed films may serve as a rigorous test of surface roughness. Be nzene condensed within the pores upon a sudden increase in P/P-s, from 0.74 to 0.84, in fair agreement with the prediction of the Kelvin equ ation for open-ended cylindrical pores with a nominal diameter of 77 A ngstrom. (C) 1998 Elsevier Science B.V. All rights reserved.