Surface topography and water contact angle of sandblasted and thermally annealed glass surfaces.

Abstract

Surface roughness has a huge influence on most tribology properties. Sandblasting is a standard way to produce surface roughness in a controlled and reproducible way. Sometimes the sandblasted surfaces are annealed to reduce the roughness and reduce the sharpness of the roughness. We study the nature of the surface roughness of sandblasted silica glass surfaces and how it is modified by annealing at different temperatures. The surface roughness decreases with increasing annealing temperature due to viscous flow of the glass driven by the surface tension. However, the skewness and kurtosis remain nearly unchanged. Optical pictures of the annealed glass surfaces exhibit cell-like structures (cell diameter ≈20-40 μm), which we interpret as micro-cracks. The concentration of micro-cracks increases with increasing annealing temperature. The micro-cracks result in a (advancing) water contact angle which decreases with increasing annealing temperature, which is opposite to what is expected from the theory if no micro-cracks would occur.