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Novel Two-Component Gels of Cetylpyridinium Chloride and the Bola-amphiphile 6-Amino Caproic Acid: Phase Evolution and Mechanism of Gel Formation
journal contribution
posted on 2012-03-08, 00:00 authored by Illa Ramakanth, Archita PatnaikA two-component gel resulting from the amphiphilic cationic
surfactant cetylpyridinium chloride (CPC) in the presence of a structure-forming
bola-amphiphilic additive 6-aminocaproic acid (6-ACA) was realized
and investigated. At a critical 6 wt % of 1:1 CPC:6-ACA, the yellow
colored gel resulted from a 3:1 v/v CHCl3:H2O critical binary solvent composition. The mixed amphiphilic system
formed a 1:1 complex with a binding constant ∼0.83 × 104 M–1. Phase evolution and mechanism of gelation
in the mixed CPC:6-ACA system was unraveled upon investigating the
gel microstructure, based on spectroscopic, microscopic, and small-angle
X-ray scattering (SAXS) investigations. The gel assembled as a lamellar
organization, maintaining a loosely interdigitated bilayer structure
of CPC and 6-ACA molecules through predominant charge transfer, H-bonding,
and hydrophobic and intercomplex interactions. The SAXS pattern indicated
a semicrystalline form to be the stable phase with alternating crystalline
and amorphous layers; a novel mode of gelation with a widely disparate
semicrystalline form of the lamellar gel was thus indicated, where
the lamellar structure was deduced from the interplanar spacings.
A transition from low viscosity reverse micellar solution to a yellow
rigid gel upon aging was thus comprehended. The mixed amphiphile in
varying polarity organic solvents in the presence of water indicated
the nonconducive nature of gelation in very highly polar solvents,
methanol, and DMF or, in very low polarity solvents, such as, cyclohexane
and carbon tetrachloride.