Adsorption kinetics of Brij 35 at air/solution interface

Dynamic surface tension and surface adsorption kinetics at the air/aqueous solution interface of dodecyl polyoxyethylene(23) ether (Brij®35, C ₁₂H₂₅O(CH₂CH₂O)₂₃H) have been investigated at different bulk surfactant concentrations and temperatures. Apparent diffusion coefficients, D_a, activation barrier, ε_a, and the adsorption kinetic parameters, n and t*, are obtained from the extended Ward and Tordai approach, and Rosen's empirical model, respectively. It is shown that Brij 35 solutions follow a mixed diffusion-activation adsorption mechanism. Results evaluated by the extended Ward and Tordai approach are consistent with those obtained from Rosen's empirical model. With increase in bulk concentration from 0.1 CMC to 10 CMC (mol/dm³), ε_a increases from 2.40 to 6.96 kJ/mol, and n decreases from 0.620 to 0.393, while with increase in temperature from 25 to 45°C, ε_a decreases from 4.59 to 3.54 kJ/mol, and n decreases from 0.534 to 0.456. This indicates that the diffusion tendency decreases with increase in the interaction between surfactant molecules while the thermo-motion of the molecules favours surface adsorption.