Physicochemistry of bis-alkyltrimethylammonium dichromate, tungstate and molybdate amphiphiles: Synthesis, characterization, behaviors at the air–water interface and self-aggregation in aqueous medium

Bis-alkyltrimethylammonium dichromate, tungstate and molybdate complexes were prepared with cationic surfactants of varied chain lengths, CnH2n+1(CH3)3N+Br−, n = 10, 12, 14, 16 and 18, by stoichiometric mixing of the surfactants with the inorganic salts (potassium dichromate, sodium molybdate and sodium tungstate) in aqueous medium and subsequent isolation by solvent extraction. They were characterized by elemental CHN analysis, nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Formation of layered structures was supported by X-ray diffraction (XRD) measurements. The phase transitions of the compounds were studied by thermo gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The low aqueous solubility of the dichromate complexes was colorimetrically determined. Monomolecular film behavior of the solvent spread dichromate complexes at the air–water interface was examined by way of surface pressure (π)–area (A) measurements. The tungstate and molybdate complexes were soluble in water. Their interfacial Gibbs adsorption and micellization behavior in the bulk were investigated by tensiometric, conductometric and microcalorimetric techniques. The size and zeta potential of the micelles were determined by the dynamic light scattering (DLS) measurements. A correlation between the hydrocarbon chain length/bivalent anions and different physiochemical properties has been established.