Role of F, Cl, Br and I in the wormlike micelles formation when combining C14TAB with 4-halogenbenzoates

Abstract

The combination of cationic surfactants with some aromatic anions can result in the formation of long aggregates, named as wormlike micelles. Like polymers, they can be used as viscosity controllers. The stabilization of the aromatic anions inserted into the micelles and their position at the surface is central to change the curvature of the aggregates and its consequent growth. Therefore, the affinity between these two components defines the potential to wormlike micelle formation and the understand of the molecular aspects that driven the process is central. In this sense, in this work it was investigated the effect of the presence of F, Cl Br or I at the position 4 of the aromatic ring of halogenbenzoates on the incorporation of the anions into the micelles of C14TAB. By using the isothermal titration calorimetry, the spontaneity of the process was determined by measuring the magnitude of the energy released and the critical concentration for wormlike micelle formation. Wormlike micelles are only formed for Cl, Br and I, and the formation is more pronounced for halogen atom more voluminous. It can be expected that the fitting into the water structure of the anion with a more voluminous halogen is more difficult. Therefore, the hydrophobic effect is an important driven force to the partitioning of the aromatic anion from water to the micellar pseudo-phase. The processes of formation, growth and shortening of the wormlike micelle chains were determined by measuring the hydrodynamic radius of the aggregates and correlated with the enthalpimetric curves. In high concentration regime, the micelles are entangled and the characteristics of the supramolecular gel-like formed were investigated by using linear and non-linear rheology.