IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Tribology Wednesday Sessions
       Session TR+SS-WeM

Paper TR+SS-WeM4
A Nanoscale JKR Test for Adhesive Contacts to Polymers

Wednesday, October 31, 2001, 9:20 am, Room 132

Session: Fundamentals of Tribology & Adhesion
Presenter: K.J. Wahl, Naval Research Laboratory
Authors: S.A.S. Asif, Geo-Centers
K.J. Wahl, Naval Research Laboratory
Correspondent: Click to Email
Contact mechanics measurements at the nanoscale are important for understanding the behavior of ultrathin films developed for adhesives, electronics packaging, microelectromechanical devices, colloidal particles, and lubrication. Determining surface mechanical properties of small devices, thin films or small volumes may be impossible by traditional methods, which lack either high spatial resolution or surface sensitivity. In this paper, we present a dynamic nanoscale Johnson-Kendall-Roberts (JKR) test to examine adhesive contacts to polymers and thin films. The nanoscale JKR test, based on a depth-sensing nanoindenter with AC force modulation capabilities,@footnote 1@ combines measurements of load and contact or interaction stiffness as a function of tip-surface separation and indenter penetration depth. With this method, and appropriate contact mechanics, it is possible to make localized mechanical property measurements (e.g. loss and storage moduli, adhesion energy, cohesive stress, and strain energy release rate) for contacts with diameters smaller than the optical limit. We present results of studies using probes with tip radii between 1 and 10 microns against polydimethyl siloxane surfaces with varying cross-link densities. Smaller probe diameters and increased cross-link density shifted the measured response away from a pure JKR model into the Maugis-Dugdale transition regime. The storage modulus and surface energy measured from nanoscale JKR results are compared to both calculated values and those measured with conventional nanoindentation. @FootnoteText@ @footnote 1@ S.A. Syed Asif, K.J. Wahl, and R.J. Colton, Rev. Sci. Instrum. 70 2408-2413 (1999).