Transmission X-ray Microscopy (TXM) Reveals 3-D Nano-structure of Clay-water Suspension

The unusual behaviour of smectites, their ability to change volume when wetted (swelling) or dried (shrinking), makes soil rich in smectites very unstable and dangerous for the building industry due to possible or likely movement of building foundations and poor slope stability. These macroscopic properties are dominated by the structural arrangement of smectites finest fraction. Here, we show in three dimensions how the swelling phenomenon in smectite, caused by a combination of hydratation and electrostatic forces, may expand dry smectite volume over 1000 times. A new technique, Transmission X-ray Microscopy, makes it possible to investigate the internal structure and 3-D tomographic reconstruction of the clay aggregates. This reveals, for the first time, smectite gel arrangement in voluminous cellular tactoid structure, within a natural aqueous environment.