Forced Wetting Dynamics of Sodium Dodecyl Sulfate Glycerol Solution on Solid Substrates

The forced wetting dynamics of a sodium dodecyl sulfate glycerol solution on both intermediate hydrophilic and hydrophilic solid substrates was studied by using the Wilhelmy plate method. The dynamic contact angle θ _D at different contact line velocities U (θ _D–U relationship) was measured. The influences of the macroscopic properties including the surfactant solution concentration, the substrate surface free energy, and the surface tension on the θ _D–U relationship were investigated, and all three properties are important. An interesting phenomenon that θ _D initially increases then decreases with U was found in the experiment, which could not be explained by modern theoretical models. The microscopic effect of the surfactant adsorption on the solid–vapor interface near the three-phase contact line was used to explain this phenomenon. A modified molecular-kinetic model was proposed, and the model can well describe the experimental results.