Effects of cationic modifier type on the structure and morphology of organo-montmorillonite and its application properties in a high-temperature white oil system

Abstract Three types (eight modifiers with three radical groups) of cationic modifiers aliphatic quaternary ammonium salts (AlQAS), aromatic quaternary ammonium salts (ArQAS), and polyoxyethylene quaternary ammonium salts (PoQAS), were used to modify montmorillonite (Mt) and prepare cationic-organo-montmorillonites (COMt). COMt was characterized by X-ray diffraction, scanning electron microscopy, contact angle, thermogravimetry, optical microscopy, gel volume, viscosity, and thixotropy to explore modifier type effects on the structure, morphology, and properties of COMt, as well as investigate the application properties in white oil system. The results show that eight cationic modifiers all entered the Mt. layer to form intercalated COMt. The modifier type significantly influences the structure, morphology, and properties of the obtained COMt and the application properties in white oil system. The basal spacing of PoQAS COMt (d001 = 4.33 nm ~ 5.28 nm) was the larger than ArQAS COMt (d001 = 3.14 nm ~ 3.60 nm) and AlQAS COMt (d001 = 2.91 nm ~ 3.66 nm). The morphologies of the three types of COMt lamella were all in a loose state. The order of COMt lamellar loosening degree with the same chain length was PoQAS COMt > ArQAS COMt > AlQAS COMt. The thermal stability and lipophilicity of the COMt powders were consistent with the morphology results. In the white oil system at 180 °C, XRD results showed that the thermal stability of PoQAS COMt was the best (maintaining the structure of PoQAS COMt and no Mt. generation), followed by ArQAS COMt, and AlQAS COMt had the worst thermal stability. The viscosity and thixotropy of three types COMt was ArQAS COMt better than PoQAS COMt and AlQAS COMt, PoQAS COMt better than AlQAS COMt. Research also showed that the steric hindrance, electropositivity of the modifier molecule, and modifiers' thermal stability are positively related to the thermal stability of COMt in white oil. This work provides a basis and other ideas in understanding the relationships between radical groups types, the structures of quaternary ammonium salts, the thermal stability of COMt, and selecting and developing new modifiers.