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

Paper TR+MM-TuP8
Nanowear Patterning as an Activated Crazing Process

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Poster Session
Presenter: R.H. Schmidt, Lund University, Sweden
Authors: R.H. Schmidt, Lund University, Sweden
G. Haugstad, University of Minnesota
W.L. Gladfelter, University of Minnesota
Correspondent: Click to Email
The friction and wear characteristics of nanoscale organic coatings are critical to new and emerging technologies (e.g. microelectromechanical devices). Fortunately the need to understand this behavior has coincided with the development of tools to measure shear forces on the nanometer scale, including the scanning force microscope (SFM). At the scientific frontier these methods have enabled careful studies of confinement effects on polymer dynamics, e.g. the glass transition. In contrast to traditional scientific disciplines like condensed matter physics and physical chemistry, the nanotribology community has only begun to examine the role of temperature in material response. The response of "soft" condensed matter to external forces can be dominated by entropic (temperature dependent) effects; further, nonequilibrium molecular conformations may introduce kinetic (rate dependent) effects. Rigorous studies of thin-film polymer nanotribology therefore must include methodologies to quantify the interrelated roles of temperature and rate. In the present work, wear on polystyrene films was studied via the commonly observed surface-patterning phenomenon, induced by raster scanning. This was examined in detail as a function of load, scan history (repetitions), scan line density, scan velocity, and temperature (40-115 ºC). Film response was highly linear with respect to load and the number of successive visits of the sliding tip. Results suggest that the scanning process induces damage in the film analogous to crazing in brittle bulk polymers. The temperature and rate dependences were analyzed within the Bingham-Voigt-Arrhenius model of plastic flow. Activation energies extracted from (a) surface roughening and (b) the spacing between scan-induced "bundles", were intermediate to known values for alpha and beta relaxations in the bulk polymer.