AFM Investigation of Epoxy Fracture Surfaces Indicating Nanoplasticity

Epoxy fracture surfaces are investigated by nanomechanical atomic-force micrsocopy (AFM). Apparent nodules on these surfaces are likely AFM tip-convolution artifacts, which might also explain apparent modulus inhomogeneities. No modulus inhomogeneities are found on smooth ultramicrotome cuts. Invest igation of a copolymer shows, however, that existing inhomogeneities can be measured indeed. AFM investigation results in plastic deformation of ultramicrotome cuts already at low forces of 50 nN, which results in a blunt topographic image and an apparently increased modulus. This suggests that thin, sharp surface features are present on ultramicrotome cuts which are plastically deformed upon AFM investigation. Super-sharp AFM imaging showed a presumably more representative image of the investigated fracture surfaces, which showed numerous depressions and vertical steps a few nanometers high. This suggests that even brittle epoxy exhibits some plasticity at the nanometer scale upon fracture