Diffusion of water in bentonite clay

Abstract

Diffusion of water confined in sodium bentonite clay is studied using the quasi-elastic neutron scattering (QENS) technique. Hydration of bentonite clay is characterized by several methods including X-ray diffraction and thermogravimetric measurements. X-ray diffraction shows that the clay is having a well-defined crystalline structure with an interlayer spacing of 13 angstrom. The QENS experiment has been carried out on hydrated as well as dehydrated clay at room temperature. Significant quasi-elastic broadening was observed in case of hydrated bentonite clay whereas dehydrated clay did not show any broadening over the instrument resolution. Analysis of QENS data reveals that diffusion of water occurs through jump diffusion. Both Jump diffusion models having random and Gaussian distribution in jump length are used to describe the observed dynamics. Obtained diffusion coefficient is found to be lower than that of bulk water.