Viscoelastic Effects in Nanometer-Scale Contacts Under Shear
NAVAL RESEARCH LAB WASHINGTON DC CHEMISTRY DIV
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We demonstrate the effects of shear modulation on the viscoelastic response of nanometer-scale single-asperity contacts under static and dynamic loading conditions. Contact stiffness and relaxation time are determined for contacts to polyvinylethylene using a scanning force microscope SFM. Knowledge of the torsional stiffness kQ of the SFM cantilever is not required to determine the relaxation time. The relaxation time was several orders of magnitude slower than the bulk relaxation time but decreased slowly to the bulk value as the sample age increased. Contacts showed no evidence of microslip. We show that the shear response observed during the making and breaking of the contacts provides information about the time evolution of the contact area that is not available in force vs. distance curve measurements.
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