## 1 Introduction  
Progress in the understanding and fabrication of surfaces with controlled wetting properties allowed the emergence of contamination free surfaces (or \"no clean\"). A familiar example is the so-called Lotus effect or ultra-hydrophobic surface, which combines multi-scale surface roughness and non wetting surface chemistry [1]. On such surfaces, droplets have minuscule contact areas and drip off easily, taking powder-like contaminants along. Conversely, self cleaning mechanisms of ultra-hydrophilic surfaces rely on the flow of the liquid film. Ultra-hydrophilic surfaces are wetted easily: if the surface is inclined, it is the flowing liquid film that carries the dirt along [2-5]. Wettability, however, is not the only desired functionality: there are many additional requirements for surfaces in day-to-day use. For most glass applications, transparency or low scatter is essential. The ultra-hydrophobic approach to glass surfaces presents a fundamental problem: the substrate roughness may hinder transparency owing to scatter losses. For self cleaning glass surfaces based on the ultra-hydrophilic approach, the most interesting, and also with respect to applications the furthest developed route, has emerged by using TiO\({}_{2}\) as a surface coating. TiO\({}_{2}\) is an example of photocatalytically active metal oxide. Under exposure to ultraviolet light, it shows extremely small contact angles of less than 1\({}^{\circ}\)[6]. The origin of this light-caused wettability enhancement is not fully understood [7,8]. The main advantage of these surfaces is the combined hydrophilicity and photodegradation effect, which significantly aids in the cleaning process. Although the ultra-hydrophilic effect is reversible in principle, the ageing of these surfaces under real conditions is not known. Recently, effort has been taken to quantify the influence of the atmospheric pollutants e.g. soiling, and ageing on the self cleaning glass functionalities [9]. In particular, pollutants that leach from siloxane based resin, which is often used to seal the glass on a frame. Such contaminants are hydrophobic and promptly spread on ultra-hydrophilic surface, resulting in a thin hydrophobic layer, which may be detrimental to the TiO\({}_{2}\) photocatalyst [10-13]. Leaching is a well known phenomenon in silicone based resins [8]. The reason is the occurrence of chemical degradation of the sealant in the first time after curing and release of siloxane oligomers during hardening that is specific for silicone chemistry. In general, formulations of curable silicone resins contain low molecular weight cross-linking agents, catalysts and plasticizers; a balance between cross-linking density and mechanical properties is often a challenge in formulation [14]. Besides that, additional processes like chain scission owing to the lability of the silicone carbon bond (Si--C) towards acidic and alkaline conditions may also occur during the initial exposure to environmental conditions. Moreover, spreading of the residual siloxane is favored on the hydrophilic SCG surface, since the TiO\({}_{2}\) surface is a high-energy one and therefore should be wetted by most liquids in particular by the low surface tension siloxane [10]. Such contaminants not only are hydrophobizing the surface but are also known to hydrolyze and condense under the influence of ambient humidity and radiation to form thin layers of SiO\({}_{2}\)[15]. It is this layer which irreversibly alters the photocatalytic activity of the TiO\({}_{2}\). In this work, we considered the possibility to prevent these hydrophobic contaminants by protecting the SCG surface with a thin sacrificial hydrogel layer. This requires a hydrophilic and water insoluble polymer layer with enhanced adhesion toward TiO\({}_{2}\) support. The polarity of the hydrogel layerfacilitates spreading of the siloxane residues and drastically reduces their adherence to the surface.