AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS2-MoA

Paper SS2-MoA1
Super Hydrophobic Interactions: From the Inside and Out

Monday, November 3, 2003, 2:00 pm, Room 327

Session: Tribology, Adhesion, and Friction
Presenter: J.E. Houston, Sandia National Laboratories
Authors: J.E. Houston, Sandia National Laboratories
S. Singh, University of New Mexico
C.J. Brinker, Sandia National Laboratories
Correspondent: Click to Email
Considerable interest has recently been directed toward the study of the processing of "super hydrophobic" (SH) surfaces and their unique properties. These materials are generally characterized by hydrophobic molecules in a fractal-like structure and have contact angle in excess of ~150. We present here studies of the behavior of the interaction force vs. relative separation between a scanning force-probe tip and sample surface using the interfacial force microscope (IFM). The measurements include "inside" interactions for both a SH film (contact angle ~165) and hydrophilic tip (~30) coming into contact with the SH surface in water, and the "outside" case for a SH-coated tip in contact with the outer water surface. As expected, the latter case shows the development of a considerable repulsive force before becoming unstable submersing the coated-tip end. However, the inside case shows a marked contrast depending on the nature of the tip. The hydrophilic tip shows only repulsive forces, as it essentially pushes against the inside surface of the water in contact with the SH film. In addition, the SH surface deformation reveals an unusual creep behavior in this case. In contrast, the SH coated tip shows large, long-range attractive forces prior to contacting the SH film, an effect which is often characterized as due to interfacial bubble formation. These results will be discussed in terms of experimental parameters, such as tip speed and the thickness of the SH film, as well as the mechanical properties of the film itself, both wet and dry. The work at Sandia was supported by the DOE Office of Basic Energy Sciences, Division of Materials Sciences. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin company, for the DOE under Contract DE-AC04-94AL85000.