Figure 8
Thermodynamics of clay swelling due to water adsorption in (a, b) Na-mica, (c, d) Li-mica and (e, f) H-mica pores. (Top row) Profiles of disjoining pressure (\(\Pi\), in kbar) and swelling free energy (\(\Delta \Omega ^{ex}\), in \(\hbox {nm}^{-2}\)) in M-mica systems. With increase in hydration energy of cations from Na\(^+\) to H\(^+\) ion, the \(\Delta \Omega ^{ex}\) progressively becomes replusive thus favouring swelling. (Bottom row) Individual contribution to \(\Delta \Omega ^{ex}\) from confined water (\(\Delta \Omega^{ex}_{ \hbox{W}}\)) and cation + mica framework (\(\Delta \Omega ^{ex}_{ \hbox{I+S}}\)). The long tail in \(\Delta \Omega ^{ex}\) for \(d \ge 11\) Å arises due to fluctuations in \(\Pi\) which can be assumed to be zero (i.e., \(\Pi (d \ge 11 {\hbox {\AA}}) = 0\)). All values of \(\Delta \Omega ^{ex}\) (individual contribution and total) were normalized by thermal energy (\(k_BT\)) and \(A_{xy}\) of mica surface used, thus has units of \(\hbox {nm}^{-2}\). The numerical value represent the energy required to separate clays of unit area (of \(\hbox {nm}^2\)) compared to thermal energy.
