Properties and Selected Applications of Microstructured Glass Devices

Abstract

The chemical stability of glasses is decisive for microfluidic, medicine and biological applications. It is characterised by the class of resistance against acids, water and lyes. The industrial standards DIN 12116, DIN 12111 and DIN 52322 provide a classification of the glasses. The chemical stability classes of the photostructurable glass FS21 are shown in Table 1.7. The durability of polished or grinded surfaces of FS21 glass sheets was further studied by eluating tests in various fluids [196]. Glass samples were removed in intervals from the fluids and dried, and the mass loss wasmeasured. The results of the eluating tests of polished samples of some square centimetres are shown in Fig. 11.1. No significant mass loss of FS21 immersed into acidic solutions, organic solutions and water was detected. However, the mass loss in alkaline solutions, such as NaOH, Tiutol, is measurable but suf- ficiently small, which is still acceptable for cleaning purposes. The mass loss of the glass in alkaline solutions increases with the duration of the immersion. The chemical attack on the ground glass samples follows the same principle; however, the mass loss is nearly twice as big as that of the polished samples. This behaviour is expected because an increase of the real surface area leads to an increase in the area for chemical interactions. It is possible to maximise the chemical stability in acidic and alkaline solutions by an additional surface coating. For instance, protective silicon nitride and silicon oxide coating are deposited using CVD-deposition [246]. These layers lead to a significantly increased durability of the glass. In particular, the silicon nitride layer leads to a much improved durability in alkaline solutions whereas the silicon dioxide layer enhances the durability against acids.