From surface to core: Exploring bulk hydrophobicity in geopolymer tiles

Abstract

This study presents a pioneering approach to produce superhydrophobic bulk geopolymer tiles (SBGT) using a novel concurrent polymerization and cold-press technique. Unlike traditional hydrophobic coatings that degrade over time, this method achieves bulk hydrophobicity by integrating fluoroalkyl silane (FAS) modification directly into the geopolymerization process. The exothermic heat released during geopolymerization was utilized to trigger a sol-gel reaction, enabling chemical grafting of the hydrophobic agent within the geopolymer matrix. The resulting SBGT materials exhibited exceptional hydrophobic properties, with water contact angles (WCA) exceeding 150°, demonstrating complete superhydrophobicity based on both static and dynamic criteria. Self-cleaning tests confirmed the high dust-repelling capability, and liquid resistance tests demonstrated strong non-wettability against common household liquids (coffee, tea, wine, and milk). Furthermore, sandpaper abrasion and water dripping tests revealed that SBGTs maintain their hydrophobicity even under mechanical stress, highlighting their long-term durability. Additionally, mechanical strength analyses showed that while moderate FAS concentrations enhanced flexural strength, excessive amounts led to a decline due to microstructural disruptions. X-ray diffraction (XRD) and scanning electron microscopy (SEM/EDX) analyses confirmed the transformation of the geopolymer into an amorphous aluminosilicate gel, reinforcing its mechanical integrity and water resistance. This is the first study to successfully implement simultaneous concurrent polymerization and hydrophobic modification in cold press geopolymer synthesis, producing a fully hydrophobic bulk material without post-processing treatments. These findings demonstrate the commercial potential of SBGTs for self-cleaning, moisture-resistant, and energy-efficient building applications.