University of Massachusetts Amherst

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"Using Contact Line – Dependent Wetting"

Date/Time: 

Tuesday, January 27, 2015 - 11:30am to 12:30pm

Presenter: 

Thomas J. McCarthy, University of Massachusetts – Amherst – PSE Department

Location: 

LGRT 201

Details: 

ABSTRACT 

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.

References

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”