Probing the formation of wormlike micelles formed by cationic surfactant with chlorobenzoate derivatives

Agradecimentos: The authors acknowledge the Brazilian agencies CNPq (grant number: 301016/2015-1), FAPESP (grant numbers: 2015/ 25406-5 and 2015/08541-6), and PETROBRAS (grant number: 2015/00103-0). We also want to thank the lab technician of the Colloids and Interfaces Group of UNICAMP, Victor Augusto Licio Garcia Vilela, for helping to perform experiments (grant number: 301016/2015-1) and Marcelo Alexandre de Farias from the Brazilian Nanotechnology National Laboratory (LNNano) for the help in the CryoTEM analysis and also LNNano to the access to the CryoTEM facilities (research proposal: TEM-24274) Abstract: The energy released when tetradecyltrimethylammonium bromide (C14TAB) is combined with different derivatives of chlorobenzoates in an isothermal titration calorimeter (ITC) allows a direct evaluation of the spontaneity of the threading of the aromatic anions into the micellar palisade. The comparison between the enthalpimetric curves with the ones for viscosity of the solutions, hydrodynamic radii of the aggregates (dynamic light scattering experiments), and the fraction of aromatic anions incorporated (diffusion-ordered spectroscopy experiments) allows the establishment of the variations of enthalpy with formation, growth, and decrease of the wormlike micelles (WLMs). The formation of WLMs with C14TAB is very favored (very exothermic) for titrations of chlorobenzoate derivatives which present the chlorine atom in positions 3 or 4 of the aromatic ring. However, the aggregation is highly unfavorable if chlorine is at position 2 of chlorobenzoate. According to the results, the high potential of the ITC to determine critical concentrations and the energies associated with the aggregation of a cationic surfactant and aromatic anions for the formation of WLMs was demonstrated FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado