Optical properties of plasma-treated PEEK: Monitoring colour and crystallinity for applications in medicine and dentistry using ellipsometry

Abstract

Poly-ether-ether-ketone (PEEK) is a widely used and versatile polymer. Here, we use ellipsometry to determine the wavelength-dependent optical properties of PEEK before and after the surface is modified by plasma immersion ion implantation (PIII), a technique that renders the surface hydrophilic and bio-active. Lorentz and Gaussian oscillator models are used to fit the data for extraction of the optical constants and the dielectric function. The effect of PIII, even for short treatment times, changes the optical properties of PEEK, indicative of an amorphisation of the initial semicrystalline structure that broadens the electronic density of states distribution. The progressive changes in the optical properties with treatment time allow assessment of colour changes and estimation of ion dose in the PIII process.