AVS 53rd International Symposium
    Surface Science Thursday Sessions
       Session SS2+NS+TF-ThA

Paper SS2+NS+TF-ThA3
Interfacial Force Microscopy of Viscous Water on Hydrophilic Surfaces

Thursday, November 16, 2006, 2:40 pm, Room 2004

Session: Tribology
Presenter: M.P. Goertz, University of Minnesota
Authors: M.P. Goertz, University of Minnesota
R.C. Major, University of Minnesota
X.-Y. Zhu, University of Minnesota
J.E. Houston, Sandia National Laboratories
Correspondent: Click to Email
The hydration of surfaces is important to many fields and its effect on system behavior has been studied for decades, yet the detailed origins of the forces involved are still under debate. We use interfacial force microscope (IFM) to measure the viscosity of water thin films with nanometer thickness on hydrophilic surfaces, including silica and carboxylic acid terminated alkanethiol self-assembled monolayers. We obtain the viscosity from this interfacial water from three different measurements: shear force measurement for a water meniscus formed between a tip and the hydrophilic surface under ambient conditions; shear force measurement for the interfaces under water; and repulsive, draining-force measurements of the two approaching interfaces immersed in water. In all three types of measurements, we obtain effective viscosities more than 10@super 6@ times greater than that of bulk water for interfacial separations on the nanometer scale. The experiments clearly show that the extent of the interphase layer and its level of viscosity depend sensitively on the strength of hydrophilic interaction, gradual degrading after the surfaces have been in water for a couple of hours. Thus, it is clear that a strong water/surface interaction gives rise to an increases in water-water bonding near the two surfaces and it is this increased level of bonding that is disturbed by the lateral tip motion resulting in the observed viscosity increase.