Synthesis, Characterization and Application of a Tetraethoxysilane–Stearic Acid Organic–Inorganic Hybrid Hydrophobizing Agent for the Water Protection of Porous Construction Materials

Abstract

Aims: The study aims to synthesise, structurally characterise and evaluate an organic–inorganic hybrid hydrophobizing agent derived from tetraethoxysilane (TEOS) and stearic acid for the long-term water protection of porous construction materials, and to verify its performance against national and interstate standards. Study Design: Laboratory synthesis of the agent followed by spectroscopic (FTIR) and thermal (TGA–DTG–DSC) characterisation, qualitative wettability testing, and standardised quantitative determination of the water-protection efficiency on real construction products. Place and Duration of Study: The study was conducted at Department of Chemical Technology, Bukhara State Technical University; standardised testing at the “Uz Test” State Institution (Bukhara branch) of the Uzbek Agency for Technical Regulation and the Bukhara Special Testing Construction Laboratory LLC. Methodology: The hybrid agent was prepared from TEOS and stearic acid by an acid-catalysed sol–gel route, using sodium peroxide (Na2O2) as an oxidising/water-releasing promoter and sulfuric acid (H2SO4) as the condensation catalyst (60–80 °C, 6–7 h). The molecular architecture was probed by Fourier-transform infrared spectroscopy (FTIR) and the thermal behaviour by simultaneous thermogravimetric–differential thermal analysis (TGA–DTG–DSC). The agent was brush-applied to fired-clay (ceramic) brick and concrete, and the hydrophobization efficiency was determined in two accredited laboratories in accordance with O’zMSt 705:2025, GOST 7025-91 and GOST 12730.2-2020. Results: FTIR confirmed a genuine organic–inorganic hybrid in which a condensed siloxane (Si–O–Si) network derived from TEOS coexists with long aliphatic chains and reactive silanol (Si–OH) groups derived from stearic acid. Thermal analysis revealed high thermal stability: only ≈2% of the mass was lost below 150 °C, the functional organic component decomposed above ≈200 °C, and a thermally robust inorganic residue of ≈52% remained, corroborating the silica-rich framework. The treated products carried discrete, spherical water droplets; the hydrophobization efficiency reached 79.0–79.1% for fired-clay brick and 80.4–81.6% for concrete, all conforming to the cited standards. Conclusion: Combining a TEOS-derived silica backbone with hydrophobic fatty-acid chains affords an effective water repellent for porous construction materials. Its water-protection performance was verified by accredited, standards-based testing, while the fluorine-free formulation based on locally available raw materials offers potential economic and environmental advantages that merit further dedicated evaluation.