Water structure perturbation by thioamides and its correlation with micellization behavior of cetyltrimethylammonium bromide in aqueous solution

The modification of water structure in the presence of different thioamides has been studied by monitoring changes in the spectral behavior of water using near infrared (NIR) spectroscopy. The analyses show that hydrogen bonding capability of different thioamides, thiourea, and thioacetamide is mainly responsible for the variation in water-thioamide interaction observed from the gradual decrease in absorbance at the combination band centered at wavenumber 6800 cm -1 . Micellization behavior of a cationic surfactant, cetyltrimethylammonium bromide (CTAB) has also been investigated in presence of these thioamides. The critical micelle concentration (CMC) of CTAB in presence of these additives has been determined by conductometric method. Steady state fluorescence quenching has been employed to determine the aggregation number ( N ). The increase in CMC (0.9 M-1.2 M) and decrease in N of CTAB (64-20) take place with the observed changes in the concentration of thioamides. The micellization behavior is influenced by thioamides mainly by following a direct action through preferential binding to the hydrophobic chain of CTAB rather than by an indirect mechanism through their alteration of water structure.