Simulation of the adsorption – desorption hysteresis for Frumkin isotherm

Abstract

A model of desorption from the surface of rotating disk into the solution of surface active substance is developed for Frumkin isotherm. The time needed to approach the first equilibrium within 1% of error is investigated. For desorption this means to acquire the highest surface coverage, and for adsorption the lowest coverage that is in the equilibrium with the bulk of solution. If the equilibrium isotherm is S shaped, the near equilibrium isotherms are characterised by big changes of coverage that are caused by small increments of bulk concentrations. These changes require very long near equilibrating times because they are driven by small fluxes of dissolved surfactant. These times are the second component of the hysteresis.