Mechanical pinning of liquids through inelastic wetting ridge formation on thermally stripped acrylic polymers.

A film composed of a thermal-stripped, solvent-borne acrylic polymer is shown to completely arrest motion of the three-phase line for water as a result of ridge structure formation. This mechanism produces anomalous wetting behavior including the arbitrary selection of contact angles, formation of quasi-periodic ridge structures on surfaces, and requirement of stick and break motion for wetting line advancement, a novel mechanism reported here. The ridges are retained by the polymer subsequent to wetting, which are 2 scales larger in height than those described previously. This allows for their characterization, which shows significant detail including the hierarchical apex structure where a cutoff area is used in theoretical treatment to avoid a singularity. Results of Wilhelmy plate experiments show a spatial connection between quasi-periodic variation in force-displacement curves and the wetting ridges on plate. These results are consistent with the dominance of the viscoelastic properties of the substrate in determining wetting behavior.