Effects of argon ion sputtering on the surface of graphene/polyethylene composites

Argon ion sputtering at various energies in the range of 500-5000 eV is performed on polymer composites of ultra-high molecular weight polyethylene (UHMWPE) with 4.6 wt% graphene nanoplatelets (GNPs). X-ray photoelectron spectroscopy (XPS) shows that irradiation above 3000 eV causes an abrupt transition from tetrahedral sp(3) into planar sp(2) carbon in the blank polyethylene surface. This graphitization process, as well as the formation of certain oxygen groups after the subsequent exposure to air, is delayed by graphene in the composites. Besides, both XPS and Raman spectroscopy indicate that a part of the sp(2) graphene network is transformed into sp(3) carbon defects by irradiation. Surface hardness and Young's modulus increase by 30-100% in blank polyethylene and the composites upon irradiation. The surface electrical resistance of polyethylene decreases from 10(15) to 10(8) Omega by sputtering at 5000 eV. Composites that are consolidated at low temperature (175 degrees C) experience a transition from insulating (10(15) Omega) to conducting (10(4)Omega) in a narrow range of Ar+ sputtering energies, while for a high consolidation temperature (240 degrees C) the transition is not observed. This research provides information on the induced interaction mechanisms between graphene and a polymer matrix upon ion beam irradiation.