Conformation–property relationships in surfactant-modified montmorillonite: effects of chain length and loading

Montmorillonite (MMT) is a layered silicate with high cation exchange capacity (CEC), but its intrinsic hydrophilicity restricts compatibility with hydrophobic polymer matrices. In this study, sodium MMT was modified using a homologous series of quaternary ammonium surfactants with varying alkyl chain lengths (C12–C18) at different CEC loadings (0.5, 1.0, 1.5 and 2.0). The structural, thermal, and interfacial properties of the organo-montmorillonites (OMMTs) were systematically examined using Fourier Transform Infrared Spectroscopy (FTIR), CHNS elemental analysis, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and water contact angle (WCA) measurements. FTIR and CHNS confirmed increasing organic incorporation with chain length and loading, while XRD revealed expansion of basal spacing up to full CEC, followed by slight contraction at higher loadings due to surfactant reorganization. TGA identified two distinct decomposition regimes corresponding to strongly bound electrostatically intercalated surfactants and excess molecules stabilized via weaker surfactant–surfactant interactions. WCA measurements revealed maximum hydrophobicity at 1.0 CEC, with longer chains (C16–C18) favoring gallery expansion but mid-chain (C14) giving optimal hydrophobicity. Using the results, we establish a conformation scheme for surfactant packing within MMT galleries, linking ion exchange, chain length and loading to hydrophobic performance. This framework offers insight for tailoring OMMTs to achieve optimal polymer–clay compatibility in nanocomposite applications.