Gradual Photochemical-Induced Conversion of Liquid Polydimethylsiloxane Layers to Carbon Containing Silica Coatings by VUV Irradiation at 172 nm

• Published in: Langmuir Vol. 25; no. 12; pp. 7129 - 7134
• Main Authors: Dölle, Christopher, Papmeyer, Marcus, Ott, Matthias, Vissing, Klaus
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 16-06-2009
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Materials: Nano-and Mesostructured Materials, Polymers, Gels, Liquid Crystals, Composites; Porous materials; Surface physical chemistry; Infrared reflection; Binary compound; High resolution; Film; Infrared absorption; X ray; Potential; Liquid layer; Density; Porous material; Silica; Solid; Energy; Technology; Force microscopy; Photoelectron spectrometry; Scanning electron microscopy; Vibration; Nitrogen; Carbon; Conversion; Infrared spectrometry; Liquid; Pore; Silicon oxides; Atmosphere; Excimer; Frequency; Smooth surface
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la900278t

Thin liquid layers of polydimethylsiloxane (PDMS) were irradiated by VUV light under nitrogen atmosphere using a Xe2*- 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 SiO2-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 SiO2. 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.