After a review of portions of our 2006-2009 research on wetting and superhydrophobicity, the use of several of the concepts of this work will be described. Experiments involving contact line pinning will be discussed that were designed using the contact line perspective of wetting and require this perspective to explain the observed results. Perspectives based on contact areas, for example, Wenzel’s and Cassie’s, are not useful in these situations. Descriptions of using thin hydrophilic contact lines to support films of water (puddles and kinetically trapped thin films) on water-repellent surfaces and to control the shape (both 2D and 3D) of these thin films and puddles will be presented. Dip-Coating deposition on both chemically and topographically patterned surfaces will be discussed. Water capillary bridges that span hydrophilic pinning features on parallel and hydrophobic surfaces are distorted by shearing the parallel plates at a low rate. The capillary bridges lengthen and distort to balance Laplace pressure (equilibrate mean curvature) as the features are separated and eventually rupture at a distance that is a function of the liquid volume, the advancing and receding contact angles of the surfaces, the separation between the parallel surfaces, and in particular, the shape and orientation of the hydrophilic pinning features. Sessile capillary bridge failure will be introduced and distinguished from tensile capillary bridge failure.
1. Gao, L.; McCarthy, T. J. Langmuir 2009, 25, 14105-14115. “Wetting 101°”
2. Cheng, D. F.; McCarthy, T. J. Langmuir 2009, 25, 14105-14115. “Using the Fact that Wetting Is Contact Line Dependent”
3. Krumpfer, J. W.; McCarthy, T. J. J. Am Chem. Soc. 2011, 133, 5764. “Dip-Coating Crystallization on a Superhydrophobic Surface: A Million Mounted Crystals in a 1 cm2 Array”
4. Wang, L.; McCarthy, T. J. Langmuir 2013, 29, 7776. “Shear Distortion and Failure of Capillary Bridges. Wetting Information Beyond Contact Angle Analysis”
5. Wang, Y.; McCarthy, T. J. Langmuir 2014, 30, 2419. “Dip-Coating Deposition on Chemically Patterned Surfaces: A Mechanistic Analysis and Comparison with Topographically Patterned Surfaces”