Efficient inhibition of montmorillonite swelling through controlling flexibly structure of piperazine-based polyether Gemini quaternary ammonium salts

Currently, it remains a great challenge to maintain clay stability in water and prevent shear dispersion of the clay lamellae. Herein, a series of piperazine-based polyether Gemini quaternary ammonium salts (QAs) with different alkyl chains and linker groups were synthesized as the novel intercalator candidates. We established the correlations between their structures and inhibition swelling behavior of montmorillonite (MMT), a representatively hydratable and expansive clay. Upon loading saturated QAs, the lateral bilayer intercalation aligning parallelly to lamella surface was validated by X-ray diffraction (XRD), namely a monolayer adsorption on MMT platelets, agreeing well with Langmuir isotherm model. By combining Fourier transform infrared (FT-IR) spectroscopy and zeta potential, electrostatic attraction and hydrogen bonding were confirmed as the crucial multiple driving forces of adsorption and intercalation. The increased water contact angles (WCAs) demonstrated the formation of protective coating for hindering the entrance of water into the interlayers of MMT. XRD and field emission scanning electron microscope (FE-SEM) indicated that, when the carbon number of "tail" groups in QAs molecules was greater than 12, the platelets of organo-MMT (OMMT) were prone to be exfoliated and aggregated parallelly to sheet surface. This study provides a unique foundation for designing the molecular structure of clay modifier.