Thermal analysis evidence for the location of zwitterionic surfactant on clay minerals

• Thermal analysis provides an insight into the location of surfactant at clays.
• The thermal behavior of surfactant on talc was similar to that of pure surfactant.
• The intercalated surfactants decomposed at higher temperature than pure surfactant.
• The surfactant intercalated into Al pillared clays via electrostatic attraction.

The exact location of surfactant molecules on clay minerals is critical for the synthesis of clay polymer nanocomposites and their applications in environmental remediation. The location and thermal characteristics of zwitterionic surfactant (Z16) composites with montmorillonite (Mt), Al13-pillared montmorillonite (AlPMt), calcined AlPMt (AlPMt/500), and talc (Tlc) were investigated by using X-ray diffraction (XRD) and thermogravimetric analysis (TG). The basal spacing of Mt was markedly increased after modification with Z16, while that of Tlc, AlPMt, and AlPMt/500 was essentially unchanged. The decomposition temperature of Z16/Tlc composite (~ 294 °C) was similar to that of the pure surfactant. Sulfobetaine apparently failed to penetrate into the interlayer space of talc; instead it was confined to external surfaces. On the other hand, the DTG pattern of Z16-modified Mt showed two main peaks (404 and 336 °C), indicating two different intercalation mechanisms of Z16 on Mt. Sulfobetaine, loaded to AlPMt and AlPMt/500, was found to decompose at 355 and 370 °C, respectively, suggesting that Z16 occupied the interpillar space in these samples. Much more Z16 was taken up by AlPMt than by AlPMt/500, although the specific surface areas of both materials were practically identical, suggesting that the surfactant molecules in the interlayer space of AlPMt were largely adsorbed by electrostatic attraction between the negatively charged groups of Z16 and the positively charged Al13 cations.

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