Influence of Salt on Cationic Surfactant-Biopolymer Interactions in Aqueous Media

The effect of the simultaneous presence of salt, sodium chloride and gelatin on micellar association structures (morphology) of cetyl trimethylammonium bromide (CTAB) has been monitored by viscosity, conductivity, Circular Dichroism (CD) spectroscopy, Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopic (FTIR) measurements. The steep rise in viscosity indicated micellar structural transitions from a sphere to higher orders in the system. CD spectroscopy revealed that gelatin has not undergone any conformational changes but induced the structural transitions in the system. Instead of a denaturing effect of the salt, the resultant gel formed was found to be stable. Electrostatic repulsion of the surfactant head groups were reduced by the screening of the halide ion that favored closer packing of the surfactant monomers. Conversely, the presence of an ion may decrease the surface charge of the micelle and thus increase the micellar packing parameter. DSC and FTIR measurements corroborated these findings.