General Theory of Adsorption Kinetics

The first physically sound model for adsorption kinetics was derived by Ward and Tordai [21]. It is based on the assumption that the time dependence of surface or interfacial tension, which is directly proportional to the surface excess F (mol m ), is caused by diffusion and transport of surfactant molecules to the interface. This is referred to as the diffusion-controlled adsorption kinetics model . The interfacial surfactant concentration at any time t, F(t), is given by Eq. (11.60), 

The above diffusion-controlled model assumes transport by diffusion of the surface active molecules to be the rate ontrolled step. The so alled kinetic controlled model is based on the transfer mechanism of molecules from solution to the adsorbed state and vice versa [20]. 

The transport of surfactant molecules from the liquid layer adjacent to the interface (subsurface) is simply determined by molecular movements (in the absence of forced liquid flow). At equilibrium, i.e. when F = Fo, the flux of adsorption is 

A qualitative model that can describe adsorption kinetics is given by Eq. (61), which affords a rough estimate and results from Eq. (11.60) when the second term on the right-hand side is neglected. 

An equivalent equation to Eq. (11.61) has been derived by Paniotov and Petrov 

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