Nanoindentation of viscoelastic materials: Mechanical properties of polymer coatings on aluminum substrates

The mechanical properties of four polymer coatings on aluminum foil substrates are examined using nanoindentation with a Hysitron Triboscope, an add-on to an AFM. In addition to static hardness and modulus measurements, the viscoelastic properties of the films, which differ in T_g and extent of crosslinking, are investigated by employing two techniques: using nanoindentation parameters to fit the creep response of the material to a one-dimensional equation based on a three-element Zener model of the viscoelastic behavior of the polymer; and fitting the creep response of the material to a previously developed, three-dimensional model of the response of a viscoelastic material to indentation by a spherical indenter. It is found that the measured static moduli are about 1.5 times greater than results of fitting creep data to the 1-D model, and are a factor of 3-6 times greater than those obtained by fits of the 3-D model.