Near-Surfaces and Bulk Modification of Silicone Rubber under UV- and Vacuum UV-Irradiation Using Excimer and Hg Lamps

The surface properties of silicone rubber can be modified by irradiation with light from the vacuum ultraviolet (VUV) spectral range of less than 200 nm. After VUV-irradiation at 185 nm with a low-pressure mercury (Hg) lamp, a reduction in residual-dust-coverage (PA fibers) of up to 80% was found. At the same time, the long wavelength UV-radiation at 254 nm of the Hg lamp causes a reduction in the optical transmission properties of the silicone bulk. The near-surface and bulk modification of optically highly transparent silicone rubber was analyzed using XPS, ATR, transmission measurements, and investigations into the reduction of the residual-dust-coverage. A comparison was made between a Hg lamp and an excimer lamp at 172 nm. The results provide valuable information for selecting the appropriate irradiation source, depending on the desired spectral range for a given application. The results indicate that excimer lamps should be preferred for optical applications in the UV-spectral range, while Hg lamps are equally suitable for applications in the visible spectral range despite low transmission losses of less than 0.5%. The irradiation dose data were obtained using a ray tracing simulation as part of these investigations to overcome limitations of UV-sensors, such as their accelerated aging and angular dependence.