DETERMINATION OF SWELLING RATES OF NAu-1 QUASI-CRYSTALS DURING CATION EXCHANGE USING ATOMIC FORCE MICROSCOPY

In situ observations of the swelling properties of the nontronite clay NAu-1 were carried out via intermittent contact Atomic Force Microscopy (AFM). Using a fluid cell, a sodium saturated sample of NAu-1 was flushed with ultra pure water, allowing osmotic swelling to occur. The system was flushed with 0.5 M KCl solution and changes in swelling were observed in 30- second intervals in real time. Due to the difference in the hydration energy of K⁺ as compared to Na⁺, an overall decrease in swelling was observed. However, changes in the d-spacing between different layers within a quasi-crystal were observed to vary from layer to layer, suggesting that mechanical forces also play a role in swelling. With this data, the swelling rates of individual layers can be directly calculated, allowing for a better understanding of the variables that govern the swelling process.