UV treatment of surfaces with excimer lasers and its effect on adhesion properties

The quality of adhesion is dependent upon the ability to apply proper surface treatment to the adherends. Both chemical modification and mechanical interlocking induced by surface treatments affect the strength and durability of the adhesive joint. Excimer laser UV irradiation presents a new technology for preadhesion surface treatment for various adherend materials. This technology presents an alternative to the use of environmentally unfriendly chemicals involved in conventional etching and abrasive treatments. The effect of UV radiation at 193 nm on polymers, composites, metals and ceramics was investigated using Scanning Electron Microscopy (SEM), Fourier Transform Infra-red (FTIR) Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS). The effect on adhesional strength and durability was tested on various joint geometries with and without exposure to hot/humid environment. Experimental results indicated that UV laser surface treatment improved significantly the adhesional shear strength, compared to untreated substrate, and was similar to or higher than that for conventionally treated substrates. Optimal UV laser treatment parameters (intensity, repetition rate and number of pulses) were defined depending on the substrate material and its chemical nature. The mode of failure changed from interfacial to cohesive as the number of laser pulses or energy increased during UV treatment until specific threshold values typical of the substrates were reached. Improved adhesion correlated with changes in morphology (uniform roughness) as indicated by SEM, with chemical modification and removal of contaminations as indicated by Auger, XPS and FTIR spectroscopies. It can be concluded that ArF UV excimer laser technology has potential as a clean and simple predhesion surface treatment for a wide range of adherend materials.