Influence of relative humidity and temperature on the sol-gel transition of a siloxane surface treatment

This work investigates the effect of relative humidity (RH) and temperature on drying phenomenon of a siloxane coating during the sol-gel process. An experimental approach was taken, due to a lack of available data in existing literature. Dynamic Vapor Sorption, Fourier Transform Infra-Red spectroscopy and X-ray Photoelectron Spectroscopy analyses were performed during sol drying, while controlling RH and temperature. The drying time increased exponentially when RH was increased. This was linked to water uptake and evaporation rate decrease, forming a more condensed coating. The thermally activated process was fitted by the Arrhenius law with an activation energy of 41.7 kJ mol⁻¹. A double exponential law was proposed to describe the time needed for drying the sol as a function of temperature and RH. Finally, differences in the gel formed were clearly demonstrated. Between a RH of 30 and 50%, the gel formation turned from a dry-before-gel to a gel-before-dry phenomenon, stressing the importance of temperature and RH control during the drying process of the sol.