Novel intercalation mechanism of zwitterionic surfactant modified montmorillonites

Abstract

In this present work, a novel intercalation mechanism of zwitterionic surfactant modified montmorillonites (ZSMMt) has been introduced. Using 3-(N,N-dimethylpalmityl-ammonio) propane sulfonate (SB16) and montmorillonite (Mt), a series of zwitterionic surfactant modified Mt were synthesized. The resulting organoclays were investigated by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), and thermogravimetric (TG) analysis, corroborated by the useful information provided by the element analysis. As revealed by XRD results, the basal spacing of ZSMMt increases from 1.47nm to 4.13nm with the increase of zwitterionic surfactant loading from 0.2 to 4.0 times of the cation exchange capacity (CEC). According to chemical composition analysis results, the number of Ca2+ ions released during the process of ZSMMt preparation is very limited and the ratios of Ca/Si and Ca/Al of ZSMMt are comparable with those of raw Mt. These results suggest that Ca2+ still remain in the interlayer spaces of Mt. There is no noticeable exchange reaction that takes place between the zwitterionic surfactant and the interlayer Ca2+. After the zwitterionic surfactant intercalation, the IR vibration shifts from 1194 to 1191cm−1, which implies a new bonding between the Ca2+ and sulfonate group of SB16. The decomposition temperature of the ZSMMt, almost 60–80°C higher than that of bulk surfactants, clearly reflects the strong interaction force after intercalation. The present study thus concludes that the intercalation mechanism of ZSMMt is not an exchange process but an ion-dipole interaction between Mt and zwitterionic surfactant, thereby, a novel cross-coupling intercalation mechanism of preparing organoclays has been proposed.