Preparation and characterization of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and hydroxyapatite (HAp) coatings using the sol-gel method

In the present study, evolution of sol-gel based coatings on the glass substrates from basic precursors: tetraethoxysilane (TEOS), methyl triethoxysilane (MTES) to hybrid systems i.e., the combination of TEOS/MTES and TEOS/MTES/HAp (hydroxyapatite) have been discussed to present a comparative study between the coatings formed. The main objective is to investigate effect of molar ratio (MR) of water on hydrolysis and precursor molar ratio to formulate effective sol and prevent phase segregation with the aim of developing stable and effective coating formulations. The coating is prepared through sol-gel processing involving hydrolysis and condensation of silane precursors, which is then combined with HAp to form a coating material in a composite matrix of TEOS and MTES and further depositing the material on glass surfaces. The study also explores microstructural evolution, thickness progression, elemental, chemical and thermal analysis of the coated samples via characterization techniques. The time of gelation is found to be affected by varying content of water, where higher water corresponds to increased rate of reaction and vice versa suggesting the need to regulate such process parameters. The microstructural analysis reveals dense structure for TEOS while globular morphology for MTES and slightly homogeneous microstructure for combined coating while TEOS/MTES/HAp shows rough and interconnected network like morphology. FTIR confirms reduced hydroxyl peak for coatings with MTES, implying induced hydrophobic character and TGA suggests increased thermal stability of TEOS/MTES and HAp incorporated coating with approximately 45% residue while TEOS coating showed 25%, MTES showed 0% and TEOS/MTES combination showed 20–25% residue.