ABSTRACT
The focus of this paper is the investigation of reduced graphene oxide (GO)/nickel foam (RGON) samples for use as supercapacitor electrodes. Nickel foam samples were soaked in a GO suspension and dried before being subjected to two different methods to remove oxygen. Atmospheric pressure annealed (APA) samples were treated with a varying number (10-18) of nitrogen plasma jet scans, where sample temperatures did not exceed 280 °C. Furnace annealed (FA) samples were processed in an atmosphere of hydrogen and argon, at temperatures ranging from 600 °C to 900 °C. Environmental Scanning Electron Microscope (ESEM) data indicated that the carbon to oxygen (C:O) ratio for APA samples was minimized at an intermediate number of plasma scans. Fourier Transform Infrared Spectroscopic (FTIR) and Raman spectroscopic data supported this finding. ESEM analysis from FA samples showed that with increasing temperatures of annealing, GO is transformed to reduced graphene oxide (RGO), with C:O ratios exceeding 35:1. X-ray Photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD) data indicated the formation of RGO with an increasing annealing temperature until 800 °C, when oxygen reincorporation in the surface atomic layers becomes an issue. Supercapacitors, constructed using the FA samples, demonstrated performances that correlated with surface atomic layer optimization of the C:O ratio.
ABSTRACT
Atmospheric pressure plasma was used to graft various biocompatible polymers to the surface of ultra-high molecular weight polyethylene (UHMWPE). Polymers used as grafts in this study were poly(2-hydroxyethylmethacrylate) (PHEMA) and polyethylene glycol (PEG). A significant decrease in contact angle was noted for grafted surfaces, indicating increased hydrophilicity. Surface functionalities were verified using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The wear properties of the coatings were determined by weight loss under conditions of a random motion pin-on-plate apparatus with the coated polyethylene plaques immersed in DI water. Based on these tests, the grafted surfaces exhibited an improved resistance to wear, compared to UHMWPE. Cell viability studies were used to confirm that the plasma treatment had no negative effects on the surface bio-toxicity. Based on the results, it is anticipated that the incorporation of these biocompatible polymer-grafted UHMWPE surfaces in metal-on-plastic orthopedic implants should improve their performance and longevity.
