Functionality mediated colour shifting gels from cetyltrimethylammonium bromide and 6-amino caproic acid

A charge transfer gel from a cetyltrimethylammonium bromide (CTAB) and an additive 6-aminocaproic acid (6-ACA), in a two-component solvent mixture at a critical solvent composition of 3 : 1 v/v water : toluene is reported. The pale yellow colour of the gel arising from charge transfer interactions between the amine group (-NH₂) of hexylamine and the ammonium ion (N⁺) of CTAB was confirmed after performing a set of trial experiments with CTAB-heptanoic acid and CTAB-hexylamine systems. The process of gelation, gel phase development and its microstructure were investigated using spectroscopy, microscopy, and small-angle X-ray scattering (SAXS) techniques. The gel formed a lamellar organization while preserving a loose-packed arrangement of a bilayer of CTAB and 6-ACA molecules, maintaining H-bonding along with significant charge transfer interactions. The SAXS pattern revealed a distinct crystalline form of the lamellar gel, indicating a stable phase characterized by alternating layers of crystalline and amorphous structures. This unique gelation nature was inferred from the interplanar spacings, demonstrating its non-conducive properties in highly polar solvents such as methanol and ethanol, as well as in less polar solvents like cyclohexane and carbon tetrachloride, when the organic solvent polarity was altered in the presence of water in the mixed amphiphilic system.