On the capillary condensation of water in mesoporous silica films measured by x-ray reflectivity

X-ray reflectivity experiments have been used to monitor the capillary condensation of water in mesoporous silica thin films. We show that both the Bragg peak intensities and the film critical wave vector transfer are very sensitive to water intrusion or extrusion from the pores. Similarly to what is achieved during adsorption and desorption of gas, adsorption isotherms can be measured by monitoring the evolution of the average electron density of the film as a function of the relative humidity. The pore size distribution of mesoporous silica thin films is further determined from the isotherms.