Atomic force microscopy of plastically deformed polyethylene subjected to tensile deformation at varying strain rates

Abstract

The surface damage induced during tensile deformation of polyethylene at different strain rates was studied by atomic force microscopy (AFM) operated in tapping mode, before and subsequent to uniaxial tensile plastic deformation. Atomic force microscopy revealed striking differences in the deformed microstructures up to the nanoscale range. The surface of undeformed polyethylene was characterised by ribbonlike fibrils of width 0·25 νm and surface features of height about 20–60 nm. Fibrils were considered to consist of microfibrils of width 0·03–0.04 νm. Small scan (30 × 30 nm) AFM images provided details of microfibrils containing chains of molecules of ~ 0·5 nm wide. Tensile deformation in the plastic region involved stretching of fibrils and microfibrils resulting in the formation of surface openings. The ability of the ribbonlike surface fibrils and microfibrils to stretch, merge, and acquire an oriented and flat structure increased with increase in strain rate in the uniaxial tensile test. Also, with increase in strain rate the chains of molecules unfold and align to produce an oriented and elongated structure. The impact of deformation on amorphous regions could only be observed at high strain rates.