Effects of sodium salicylate on didecyldimethylammonium formate properties and aggregation behaviors

The effects of addition of sodium salicylate (NaSal) on micellar solutions of didecyldimethylammonium formate (DDAF) were investigated by equilibrium surface tension, wetting measurements and dynamic surface tension. The experimental results showed that the critical micelle concentration (cmc) values of DDAF aqueous solutions decrease in the presence of NaSal. It could be concluded that the net structure among Sal − ions formed by intermolecular hydrogen bonds (O H O) caused the diffusion rate slowing down from bulk phase solution to subsurface at the very beginning for a few seconds. These could be also reflected on the increase of contact angle and dynamic surface tension at first. The addition of the structure-forming agent sodium salicylate could induce the phase transformation from wormlike micelle to vesicle in aqueous solution with the molar concentration ratio of DDAF/NaSal ranging from 7/3 to 8/2. In addition, the package of Gaussian09 was applied to explore some weak interactions, such as hydrogen bonding of NaSal and electrostatic interactions. We found that the strength of intramolecular hydrogen bonding (O H O) of NaSal is reduced by electrostatic interaction, which would contribute to the formation of intermolecular O H O bonding between NaSal molecules. The existence of these weak interactions could be also confirmed by UV–visible spectroscopy and FT-IR.