Morphology of porous media studied by nuclear magnetic resonance

Abstract

The filling processes of water and cyclohexane in porous silica (40 Å, 60 Å and 112 Å pore size samples) were studied using T2 nuclear magnetic resonance (n.m.r.) experiments. The silica pores contained water or cyclohexane and the experiments were performed at room temperature and at filling fractions ranging from 0.02 to 1.0 (that is, completely full). Two distinct processes were observed which depended on the hydrophilicity of the silica surface (or the surface adhesion of the liquid). Water was found to collect in small puddles in the silica interstices, and to form a surface layer over the silica before the remaining pore volume was filled. Water in a surface-treated porous silica and cyclohexane in regular porous silica appeared to completely fill the smaller before the larger pores, and not form a separate surface-coating layer. This work also presents the techniques used to calculate quantitative information about the filling process; specifically, determination of the volume to surface-area ratio of the liquid puddles as well as the number of these puddles, is demonstrated.