Dynamic Wetting of Hydrophobic Polymers by Aqueous Surfactant and Superspreader Solutions

In this paper, we comparatively investigated the wetting performance of aqueous surfactant solutions in a wide range of concentrations, including conventional ionic surfactants (CTAB, SDS) and two nonionic polyether-modified trisiloxane surfactants (TSS6/3, TSS10/2), over hydrophobic polypropylene substrates. In all cases, scaling analysis of the experimental data of spreading drops showed that the early spreading stage was dominated by inertia and that the duration of this stage was not influenced by the addition of surfactant. For conventional surfactant solutions, we only observed the inertia-dominated spreading stage before the drops stopped wetting with a finite stable contact angle. For both trisiloxane surfactants, after the inertial stage we observed a second viscosity-dominated spreading stage. In this stage, TSS10/2 showed an enhanced wetting capability independent of its concentration, while TSS6/3 started to show a concentration-dependent spreading behavior that was fully developed in a third superspreading stage. Our findings suggest that the superspreading property of TSS6/3 began to take effect after a characteristic time, before which the superspreading TSS6/3 and the nonsuperspreading TSS10/2 behaved similarly. Power law fits to the superspreading regime are in agreement with an interpretation of Marangoni flows resulting from surface tension gradients.