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.