Speakers
Description
Soda-lime-silicate (SLS) glass is widely used in industry. To render its surface hydrophobic, it is commonly modified using different silane derivatives. Among the most widely used are alkoxysilanes, which can be anchored onto the glass surface through hydrolysis, followed by condensation between the silanol groups of the silane and those on the glass surface. Among the alkoxysilanes, tetraethoxysilane (TEOS) is unique because, after complete hydrolysis, it contains no organic groups and only OH groups attached to the Si atom. This also makes TEOS an excellent glass surface modifier, since it increases the number of active silanol groups on the glass surface, thereby making it susceptible to a higher degree of modification.
In this work, we investigated how the modification of SLS glass with hexadecyltrimethoxysilane (HDTMS), and consequently its hydrophobicity, is affected when TEOS with different degrees of hydrolysis is used as the first glass layer. In this way, a sandwich structure was built in which the first layer on the glass consisted of TEOS, onto which HDTMS was chemisorbed. The analysis was performed by recording FTIR specular reflectance spectra, from which IR reflectance–absorbance spectra and two-trace two-dimensional correlation spectra were obtained. This analysis is particularly interesting because it provides information on the IR spectra of the formed ultrathin siloxane film on top of the glass substrate, both of which possess very similar chemical structures.
The morphology of the films was analyzed using Atomic Force Microscopy, while the wetting properties were determined through measurements of the water contact angle and the calculated polar and dispersive components of the surface energy using the Owens–Wendt–Rabel–Kaelble (OWRK) method.
The obtained results show that the degree of hydrolysis of TEOS strongly depends on time, pH, and the solvent used. It will be shown that drying and curing play particularly important roles in the hydrophobicity of the modified glass, which is in connection to the content of surface silanol and siloxane groups. The hydrophobicity of the glass resulting from modification with a second HDTMS layer in each case will also be discussed.
Keywords: soda-lime-silicate glass; hydrophobicity; tetraethoxysilane; hexadecyltrimethoxysilane
Acknowledgement: This work was financially supported by the Ministry of Education and Science of the Republic of North Macedonia under National Project No. 15–6171/36.