Kinetics of adsorption at liquid/liquid interface. Role of diffusion, energy barrier and number of free sites when the desorption in slight

Abstract

The general equation describing the adsorption kinetics at an interface may be simplified when the desorption is slight. The number of solute molecules lying at the interface, at any time is given by the relation, n= 2C₀(Dt/π)^½(S_S/S) exp (ε_b–ε_a)/kT. The quantity 2C₀(Dt/π)^½ comes from the diffusion equations, whereas S_S/S brings in the fraction of free interface and exp[ε_b–ε_a/kT] is the transfer probability of a solute molecule over an adsorption energy barrier. The introduction of an interfacial equation of state allows one to test this theory with the experimental results obtained, with the aid of a pendant-drop tensiometer, for chlorophyll adsorbing at the paraffin oil/water interface. The influence of the temperature and of the introduction of a second polar solute (lauric alcohol) with the adsorption kinetics is studied.