Effect of Sodium Salicylate on the Formation and Properties of Wormlike Micelles in Aqueous Cationic Gemini Surfactant Solutions

The effect of sodium salicylate (NaSal) on the formation and properties of wormlike micelles in aqueous solutions of 2-hydroxyl-propanediyl-a,.-bis(dimethyldodecylammonium bromide) (12-3(OH)-12) and propanediyl-alpha,omega-bis(dimethyldodecylammonium bromide) (12-3-12) at a surfactant concentration of 50 mmol . L-1 was investigated using steady-state and frequency sweep rheological measurements. In the absence of a salt, 12-3(OH)-12 or 12-3-12 only produced spherical or small rod-like micelles at 50 mmol . L-1. The addition of NaSal promoted micellar growth yielding wormlike micelles in both systems. 12-3 (OH)-12 showed a more sensitive response to the added NaSal compared with 12-3-12 and formed wormlike micelles at relatively lower salt concentrations. Moreover, the wormlike micelles formed by 12-3 (OH)-12 were longer than those formed by 12-3-12, resulting in higher viscosity for the former solution. These were attributed to the hydrogen bonding interactions between the hydroxyl substituted spacers in the 12-3(OH)-12 system, which increased hydration on the aggregate surface and stimulated the dissociation of counterions. The higher charge on the 12-3(OH)-12 micellar surface was strongly associated with Sal-, which led to a tighter packing of the surfactant molecules in the micelles and thus strengthened the intermolecular hydrogen bonding interactions and effectively reinforced the growth of the 12- 3(OH)-12 micelles.