USE OF A SCANNING PROBE MICROSCOPE TO MEASURE MARRING MECHANISMS AND MICROHARDNESS OF CROSS-LINKED COATINGS

A scanning probe microscope (SPM) was equipped with a high-modulus pro be to indent coating surfaces when normal force is applied. A method f or measuring microhardness with this probe is described. The high-modu lus probe was also used to mar coating surfaces under controlled condi tions by application of normal force plus lateral motion. Dimensions o f the mars were measured by conventional scanning probe microscopy. Th e data were analyzed in terms of a ''three response, two mechanism mod el'' of marring in which three types of responses of polymeric materia ls: elastic, plastic deformation, and fracture, are measured. Of the t hree responses, only plastic deformation and fracture result in marrin g, and the two mechanisms can be quantified. A fourth quantity which c ombines plastic deformation and fracture is suggested as a method of c omparing ''micro mar resistance'' of materials under specified conditi ons. Three crosslinked polymeric coatings were studied in detail. Two had hard crusts of material near their surfaces that responded quite d ifferently than the bulk of the material.