1. Time-dependent Dynamic Receding Contact Angles Studied during the Flow of Dilute Aqueous Surfactant Solutions through Fluorinated Microtubes
Anyfantakis et al., Chem. Lett. 201241, 1232

2. Influence of surfactants in forced dynamic dewetting
F. Henrich, D. Fell, D. Truszkowska, M. Weirich, M. Anyfantakis, T.-H. Nguyen, M. Wagner, G. K. Auernhammer* and H.-J. Butt
Soft Matter2016, DOI: 10.1039/c6sm00997b 

The dynamic wetting of liquids has gained increased research attention due to its fundamental interest as well as practical importance in numerous technologies. Especially the wetting of complex fluids is an exceptionally challenging but particularly complex case...

We have recently investigated the time-dependent dewetting behavior of dilute CTAB solutions during forced flow in fluorinated ethylene propylene microtubes [1]. We have demonstrated that the surfactant solution-solid contact time strongly affected the dynamic receding contact angles, leading to unexpectedly slow kinetics (up to several hundred s). The final state displayed a zero degree contact angle. Control experiments showed that this effect is absent in simple (one-component) liquids, where the dynamic receding contact angle remained constant with increasing solid-liquid contact time (figure below). 

In a plethora of practical applications, such as coatings, detergents and those involving imbibition of liquids in porous materials, liquid wetting needs to be precisely controlled. A common approach is to add surfactants in order to lower the surface tension of the liquid. Nevertheless, surfactant addition makes the wetting process more complex, because time-dependent phenomena, i.e. surfactant adsorption at all available interfaces, come into play.

We developed a simple experimental configuration to study the dynamic wetting/dewetting of surfactant solutions that are forced to flow through transparent microtubes (figure above). By means of different optical microscopy techniques, we were able to directly measure the dynamic advancing and receding contact angles of moving liquid slugs, as well as the flow patterns withing the wetting liquid.‚Äč

Dynamic Wetting of Surfactant Solutions