A calorimetric study of mesoscopic swelling and hydration sequence in solid Na-montmorillonite

Thermoporometry, a calorimetric technique, has been applied on solid montmorillonite samples at variable relative humidity (RH) and brings novel information on the swelling mechanism of Na-montmorillonite. Some mesopores are already filled with water in conditions where the interlamellar space is only occupied by one layer of water molecules. It was also shown that inter-particles osmotic swelling in the mesoporous range begins at a lower RH than in the interlamellar space (54% and 80%, respectively) and present a large range of expansion (from 2.25 nm to 4.00 nm in the investigated RH domain). This inter-particles swelling plays therefore a dominant role in the overall swelling process in a broad range of RH values. Combining thermoporometry with XRD results, the results were integrated in a complete hydration sequence for Na-montmorillonite.