AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoM

Paper SS3-MoM3
Probing Interaction Potentials Between Surfaces in Water

Monday, October 2, 2000, 9:00 am, Room 210

Session: Surface Science Opportunities and New Applications
Presenter: J.G. Kushmerick, Sandia National Laboratories
Authors: J.G. Kushmerick, Sandia National Laboratories
B.C. Bunker, Sandia National Laboratories
Correspondent: Click to Email
Adsorbed water layers are known to strongly mediate interactions between non-ionic surfaces. These so-called hydration forces control processes as diverse as protein folding and the undesired adhesion between hydrophobic surfaces in micromachine components. Until recently, most investigations of hydrophobic interactions have been performed using the surface forces apparatus and atomic force microscopy. The former technique is limited to investigations on extended mica surfaces, while the latter technique is limited to probing only the outer regions of force-distance profiles due to "snap-to-contact" problems. The difficulties associated with making localized measurements of the hydration force have now been overcome using an interfacial force microscope (IFM), which allows force-distance profiles to be obtained at sub-nanometer resolution until the tip and surface are in intimate contact. Experiments have been performed in humid atmospheres and under water. Examples of IFM investigations of hydration interactions are provided for a range of hydrophobic-hydrophilic tip-substrate combinations prepared using functionalized self-assembled monolayers (SAMS). Investigations have also been performed on SAM coatings used to control stiction in micromachines and on polymeric coatings such as poly n-isopropyl acrylamide that can be switched between hydrophilic and hydrophobic states. Results on the polymers indicate that adhesive interactions can be modified by at least an order of magnitude by conformation changes associated with the adsorption and desorption of water. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-ACO4-94Al85000.