Hydrophobic Glass Coated with Surface Modified-Silica Film Prepared From Sodium Silicate

Abstract

In this paper, we report on the hydrophobic coating of glass substrate with silica gel film based on sodium silicate solution as the starting material. The silica gel film was formed by dip coating and drying at room temperature. The silica gel film was made hydrophobic by surface modifying agent, either using hexamethyldisiloxane (HMDS) or trimethylchlorosilane (TMCS), by solvent exchange method. We found that the drawing speed during dip coating and the initial concentration of silica had no significant effect on the hydrophobicity of the silica gel film. The hydrophobicity was measured by measuring the contact angle of water on the film. However, the contact angle is greatly influenced by the conditions during surface modification such as the concentration of surface modifying agent and the contact time. A high contact angle of 142.5° can be obtained by modifying the silica gel film in 9.7 M TMCS solution at 50°C for 7 hours. The transparency of the surface-modified silica gel film, measured as the %transmittance using a spectrophotometer, slightly decreases compared to the glass substrate. On average, they take the value of greater than 93.5% relative to that of the glass substrate. 1. Introduction Hydrophobic surfaces have considerable technological potential for various applications due to their excellent water-repellent properties. One of them is the self-cleaning application including self-cleaning windows, windshields, exterior paints for building, roof tiles, textiles, and drag reduction in fluid flow. Hidrophobic surface are those on which the water contact angle is between 90-150 degrees. Lotus leaf is a classical example of natural super-hydrophobic surface on which the contact angle of water is larger than 150 degree. The super-hydrophobic and self-cleaning surface effects of lotus leaf and other plant leaves such as rice and Indian cress is caused by the rough structure [1]. The increasing interest in studying and manufacturing hydrophobic surface results from their possible practical applications. They find their primary use in corrosion, erosion or general degradation protection applications on metallic, polymer and inorganic oxide (stone, glass, ceramic, etc.) solid surfaces. In recent years, this field has evolved into a major industry trade which covers modern applications from anti-fogging as well as water and snow repellent surfaces for construction materials, glass, automotive and aerospace technology, all the way to reducing frictional drag on airplane wings and ship hulls [2]. Glass coated with silica using tetraethylorthosilicate (TEOS) as the silica source can make the glass surface hydrophobic and has a self-cleaning effect [3,4]. Self cleaning is the key advantage which keeps the surface clean while rain water beads up and rolls over these surface entrapping dirt and particulates. The use of an expensive material such as TEOS hinders their practical applications. In this work we report on a sol-gel derived method for coating glass substrate with a thin film of silica by dip coating. The coating materials use sodium silicate as a silica precursor and trimethylchlorosilane (TMCS) or hexamethyldisilazane (HMDS) as the surface modifying agent. The use of cheap and non-toxic silicate precursor must be preferable than its counterpart alkoxide compounds in the frame of environmentally friendly processes.