The different subjects of adsorption kinetics and relaxations at

The Different Subjects OF Adsorption Kinetics AND Relaxations AT Interfaces 

Before starting with the description of present theories of interfacial relaxations, the difference from adsorption kinetics studies has to be pointed out. The general difference lies in the composition of the adsorption layer. Adsorption kinetics processes, described in previous chapters usually start from an uncovered interface. The species with the highest concentration and surface activity adsorb first. The best measure to estimate the rate of adsorption at the beginning of the process is the ratio of surface concentration r over bulk concentration c. To compare the adsorption rate of two surface active compounds a simplification of Eq. (4.85) can be used, from which the time t needed by a surfactant to reach 95% of the equilibrium adsorption results. 

This adsorption time of course, does not represent the time necessary to establish adsorption 

the first estimation of the characteristic adsorption time is obtained from 

Typical values of the diffusion coefficient and the maximum surface concentration are D = 510 cm /s and = 5T0 mol/cm. The characteristic adsorption time of a sodium octyl sulphate with aL=3.510 mol/cm results to t j 0.00004 s, for sodium dodecylsulfate tgd 0.009 s, more than two orders of magnitude higher (cf. Appendix 5D). 

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