Mobility of Water Adjacent to Mineral Surfaces

Mobility of water adjacent to Na‐ and Ca‐saturated bentonite surfaces was estimated from diffusion rates of deuterium hydroxide in oriented clay pastes at several moisture contents. The first molecular layer of adsorbed water on Na‐ and Ca‐clays had mobilities which were 30 and 5%, respectively, of the mobility of water molecules in bulk water. There was an indication of a slight reduction in mobility of water as far as 40Å. From the sodium‐saturated clay. However, water more than three molecular layers from the solid surface had mobilities which were 60% of the mobility in bulk water. The mobility data indicate that water outside the first adsorbed molecular layer does not have viscosities more than 2.5 times the viscosity of bulk water.