Electrochemical control of montmorillonite clay swelling
Abstract
The swelling–shrinking behaviour of a montmorillonite clay film in aqueous electrolyte solutions has been monitored using quartz crystal resonators. The resistance of the electrically equivalent circuit for the clay-coated resonator, which is increased by the clay swelling, was evaluated through impedance measurements. When NaCl, MgCl2 or AlCl3 were used as the electrolyte, the concentration of cation at which the film swelling occurs (transition concentration) was lower for a cation possessing a larger charge. In an FeCl3 solution, the transition concentration was raised by reducing Fe3+ to Fe2+ electrochemically. Further, in a 10–4 mol l–1 FeCl3 solution, the clay film was swollen by reducing Fe3+ to Fe2+ and was then shrunk by oxidizing Fe2+ back to Fe3+; the swelling–shrinking behaviour was electrochemically controlled.