Inhomogeneous Distribution and Collective Diffusion of Solution Molecules in the Nanochannel of Mesoporous Silica

Abstract

13C NMR spectra were observed for the mixed solutions composed of 2-propanol and cyclohexane in contact with a mesoporous silica, MCM-41, to study the distribution and dynamics of these molecules in the nanochannel of MCM-41. From the analysis of the spectral and relaxation data, we deduced that a high concentration gradient exists in the radial distribution of these liquid molecules in the nanochannel: alcohol molecules prefer the region near the surface and cyclohexane molecules the central portion of the nanochannel. Further evidence for this new model have been obtained by the spin-probe ESR observations. In addition, we obtained a model for the movement of solution molecules in the nanochannel: molecules “flow or diffuse collectively” by slipping on the channel surface.