3-aminopropyltriethoxysilane (APTES) coating of glass surface using supercritical CO2: A solvent-free approach

A sustainable alternative to conventional silanization techniques has been investigated with supercritical carbon dioxide (scCO 2 ) as a solvent for 3-aminopropyltriethoxysilane (APTES) deposition on glass surfaces. APTES deposition behavior was systematically evaluated under varying operational parameters, including pressure (90 and 150 bar), temperature (100-140°C), and reaction time (3 and 5 hr). FTIR spectroscopy, atomic force microscopy (AFM), and drop shape analysis (DSA) were employed to assess the chemical modifications, surface morphology, and wettability of the coated glass. Results demonstrated that temperature and pressure significantly govern the coating process, with increased pressure positively correlating with APTES deposition while elevated temperatures (100°C to 140°C) reduced deposition efficiency. AFM analysis revealed that surface roughness (Ra) increased progressively with higher pressure and longer reaction times, ranging from approximately 0.7 nm for lightly treated surfaces to over 10 nm for heavily coated samples. This confirmed the transition from uniform coatings to agglomerated surface structures at higher operating conditions. Surface energy determination demonstrated that the dispersive component of the surface energy consistently dominated, while the polar component varied with temperature, indicating a temperature-dependent modification of the surface functionalities. The density of scCO 2 emerged as a critical factor affecting surface deposition, with maximum deposition occurring within the 281-333 kg/m 3 density range. Notably, complete silanization reactions and homogeneous surfaces were achieved primarily at lower scCO 2 densities. • Solvent-free APTES coating on glass was achieved using supercritical sCO 2 . • Deposition mass and surface roughness are controlled by sCO 2 density and time. • Uniform coating achieved low operating conditions (e.g. 90 bar and 3 hr).