The influence of alkyl chain length on surfactant distribution within organo-montmorillonites and their thermal stability

Organically modified clay minerals with high thermal stability are critical for synthesis and processing of clay-based nanocomposites. Two series of organo-montmorillonites have been synthesized using surfactants with different alkyl chain length. The organo-montmorillonites were characterized by X-ray diffraction and differential thermogravimetry, combining with molecule modelling. For surfactant with relatively short alkyl chain, the resultant organo-montmorillonite displays a small maximum basal spacing (ca. 1.5 nm) and most surfactants intercalate into montmorillonite interlayer spaces as cations with a small amount of surfactant molecules loaded in the interparticle pores with "house-of-cards" structure. However, for surfactant with relatively long alkyl chain, the resultant organo-montmorillonite displays a large maximum basal spacing (ca. 4.1 nm) and the loaded surfactants exist in three formats: intercalated surfactant cations, intercalated surfactant molecules (ionic pairs), and surfactant molecules in interparticle pores. The surfactant molecules (ionic pairs) in interparticle pores and interlayer spaces will be evaporated around the evaporation temperature of the neat surfactant while the intercalated surfactant cations will be evaporated/decomposed at higher temperature.