Alkali-activated organogeopolymers with volumetric superhydrophobicity

A novel class of hybrid organogeopolymers with tunable volumetric superhydrophobicity was developed via a scalable and catalyst-free route. Its synthesis integrates alkali (NaOH) dissolution of metakaolin, hydrolysis of methyltrimethoxysilane, and hybrid co-condensation of the resulting silanols (Si(OH)4), sodium-aluminols (NaAl(OH)4), and methyltrihydroxysilanes (CH3Si(OH)3). Results of molecular structure analyses via X-ray diffraction, small-angle X-ray scattering, nuclear magnetic resonance, and Fourier-transform infrared spectroscopy validate the successful generation of an amorphous inorganic backbone consisting of tetrahedral SiO4/2 and NaAlO4/2 units existing in traditional, purely inorganic geopolymers, but with newly added terminal tetrahedral organic (–O3/2SiCH3) radicals, which perturb the continuous polycondensation, reduce long-range ordering, and introduce micro/nano-pores via hydrophobic aggregation and micelle formation. The unique combination of multiscale pores and nonpolar methyls lining the pores renders the organogeopolymers three-dimensional superhydrophobicity that can be tuned by varying the T/Q (where T and Q are tri- and tetra-functional siloxanes respectively) ratio. For the studied organogeopolymers with a variable T/Q molar ratio of 0.02–0.11, but fixed Si/Al and Na/Al molar ratios of 1.70, and 1.00 respectively, the water contact angle increases from 10 to 169°, while the compressive strength decreases from ∼9.8 to 0.5 MPa. The material loses its superhydrophobicity upon heating to ∼370 °C.