Impact of wettability on moisture transport at mesoscale in porous materials

Abstract

A multiscale NMR method is used for probing the proton dynamics in control pore glasses (CPG) standing in the meso and macro scale ranges. The porous material has been synthetized in our laboratory following the sol–gel route as well as spinodal decomposition. Special heat treatment has modified the proton species at the pore surface. 1H high field NMR spectroscopy has been realized under controlled relative humidity conditions. This has allowed a clear identification of the different proton species present during the kinetics of hydration from RH=0% up to 98%. We focused on the nuclear magnetic relaxation dispersion experiments to probe specifically the proton dynamics in CPG pores with and without methyl groups at the surface. A detailed analysis of the frequency dependences of the longitudinal relaxation rates in these two materials evidences the impact of microscopic wettability on moisture transport in meso- and macro-porous materials. The surface modification has allowed a frequency rescaling such that different regimes of relaxation dependence can be fully explored in a larger frequency range than that explored by FFC relaxometry. We believe that such an NMR study realized on model porous materials is of particular importance for studying the moisture transport between the meso- and macro-porous networks of cement-based materials.