Surface engineering for the control of polyethylene terephthalate (PET) wettability characteristics using laser beam wavelength

The science and technology behind using laser beam wavelength and the subsequent manipulation of a material’s polar component (through atmospheric oxygen content) to design and control the contact angle behaviour of the surface of polyethylene terephthalate (PET) is presented. The findings indicate that the theory will be applicable to most polymers. When exposed to infrared (IR) CO2 laser irradiation the PET surface experienced no change in chemistry and, therefore, no change in polar component occurred. There was, however, topography change to produce a rougher surface; consequently, advancing contact angle followed the Wenzel, etc. theories and increased, changing the surface from hydrophilic to hydrophobic. In contrast, ultraviolet (UV) KrF excimer laser beam radiation altered both the topography and chemistry of the PET surface. The very nature of processing polymers with UV laser radiation inherently generates a surface that is more oxygen-rich with enhanced functional groups, which cause an increase in its polar nature. This UV laser irradiation–induced enhanced polar nature has more of an effect than topography for polymers, which, in turn, effects a decrease in advancing contact angle. In this instance the PET surface became more hydrophilic. There is now movement towards a new science-based platform from which to assess, research and establish the methodologies for wettability characteristics design and modification through controlled laser beam exposure.