Novel insights into the self-assembly behaviors of cationic surfactant and bivalent acid: Effects of group positions in bivalent acid

The effects of carboxylate group positions in terephthalic acid (TA) and phthalic acid (PA) on the self-assembly behaviors of cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) have been investigated by interfacial tension (IFT) measurement and molecular dynamics (MD) simulation in this study. The IFT results reveal the added PA improves the interfacial activity of DTAB more effectively than TA at acid/NaOH molar ratio of 1:2. The number density profiles in MD simulation systems are calculated to confirm the high interfacial adsorption in DTAB/PA2− system. Interaction energy calculation and molecular electrostatic potential analysis demonstrate the ortho-position distribution of carboxylate groups enhance the electrostatic potential more obviously, which results in the more stable gemini-like self-assembly configurations in DTAB/PA2− system. Spatial distribution function calculation and reduce density gradient method are employed to further visualize the intermolecular interaction between DTAB and acid molecules. The present study provides the visual insights into the effects of functional group positions in acids on their self-assembly behaviors and intermolecular interaction with cationic surfactant.