Polymer fracture and deformation during nanosectioning in an ultramicrotome

The fracture and deformation behaviour of a thermoplastic in the nanosectioning process is investigated by using an ultramicrotome instrumented with force transducers. For sections with thickness values in the order of 10-100 nm, the specific work of surface formation of polymethyl methacrylate is found to be 6.3 J m(-2), which is considerably smaller to macroscopic fracture toughness, but relatively close to the theoretical specific surface energy of 1.5 J m(-2) of breaking the covalent bonds. Periodic transverse features, spaced a few hundred nanometres on the sectioned surfaces, are observed by atomic force microscopy for sections above a critical thickness. It reveals that a transition of the deformation mode occurs at a certain thickness, which is in concert with sectioning experiments for other materials showing adiabatic shear bands. (C) 2017 Elsevier Ltd. All rights reserved.