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Thin liquid layers of polydimethylsiloxane (PDMS) were irradiated by VUV light under nitrogen atmosphere using a Xe(2)- excimer lamp. The irradiated layers were analyzed with infrared reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS), showing a gradual photochemical-induced conversion of the liquid PDMS to solid SiO(2)-like coatings. IRRAS measurements revealed a smooth frequency shift of the maximal absorption band from 1111 to 1231 cm(-1) with increasing irradiation energy density caused by a gradual shift from the asymmetric Si-O stretching vibration of PDMS to the longitudinal optical (LO) mode of SiO(2). The shift was found to be dependent on the applied irradiation energy density and the O/Si ratio in the film analyzed by XPS measurements. The atomic ratio of O/Si increases from 1:1 to about 2.5:1. At the same time, the atomic ratio of C/Si decreases from 2:1 down to 1:6.5. Images taken by high resolution field emission scanning electron microscopy (FESEM) and scanning force microscopy (SFM) show a smooth surface without cracks or pores. The controllable coating properties in combination with the possibility for local irradiation using masks are promising high potential for the coating technology.

The crosslinking of thin liquid PDMS layers by three different technically relevant processes, H2 radio‐frequency plasma treatment, Xe2* excimer VUV irradiation, and low‐energy electron beam processing is investigated. The modifications to the layers due to the processing are monitored by means of RAIRS. Plasma processing of liquid PDMS leads to a direct conversion to a SiOx‐like material of the topmost layers, whereas a gradual transition from PDMS to the same product is observed upon VUV irradiation. Electron exposure does not induce oxidation. The initiating steps of the conversion induced by the interaction with VUV photons, low‐energy electrons, or their combined effect with ions and H atoms in the plasma are discussed. The latter creates a high density of damage sites. magnified image

Photocatalytic TiO 2 layers prepared by PVD or CVD processes are already produced industrially. The deposited TiO2 needs a sufficiently high concentration of the photocatalytically active anatase phase which is produced at higher substrate temperature. As a consequence, the PVD/CVD techniques are limited to heat-resistant substrates. A novel approach for plasma hybrid coating technology is presented here using the advantages of a cold low-pressure plasma process in combination with non-reactive siloxane (polydimethylsiloxane -PDMS) dispersions containing sub-micron TiO2 particles for surface functionalisation. As the result, a mechanically stable composite film containing TiO2 particles with a diameter of up to several times the average coating thickness is generated. The film consists of a top SiO2-like surface layer and, depending on the initial film thickness, an underlying gradually demethylated and crosslinked siloxane. Although the TiO2 particles are partially covered by a thin matrix layer of several nanometres, the thin coating shows photocatalytic activity as demonstrated by UV-degradation of methylene blue. The photocatalytic activity depends on the TiO2 particle concentration in the film and can be further enhanced by exposing the TiO2 surface by CF4 plasma etching of the composite film.