A new interpretation of the mechanism of wormlike micelle formation involving a cationic surfactant and salicylate

• Published in: Journal of colloid and interface science Vol. 552; pp. 794 - 800
• Main Authors: de Souza, Renato Nunes, Jora, Manazael Zuliani, Duarte, Luís Gustavo Teixeira Alves, Clinckspoor, Karl Jan, Atvars, Teresa Dib Zambon, Sabadini, Edvaldo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.09.2019
• Subjects: Calorimetric titration of salicylate with TTAB; Mechanism of wormlike micelle formation; Probing micellar aggregates by fluorescence life-time of salicylate; Probing micellar aggregates by fluorescence life-time of salicylate; Calorimetric titration of salicylate with TTAB; Mechanism of wormlike micelle formation
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2019.05.025

[Display omitted] When tetradecyltrimethylammonium bromide, TTAB, is added to aqueous solution of sodium salicylate, NaSal, the threading of the aromatic anion into the micellar palisade leads to the formation of wormlike micelles. Based on the calorimetric titration of NaSal with TTAB, and on the lifetime of fluorescence of salicylate, we propose that the aggregation of the two components directly leads to the formation of wormlike micelles, without any pre-aggregation. By using an isothermal titration calorimeter, aliquots of TTAB were added to a dilute solution of NaSal. The energy involved in each addition was then integrated and the variation of enthalpy was determined. In the same range of concentrations and molar ratios, the surface tensiometry and time-resolved emission spectroscopy experiments were performed. A very characteristic calorimetric signal associated with wormlike micelle formation was obtained, being the enthalpy variation of this process, ΔWLMH2980 < 0. When 1.2 mmol L−1 of NaSal is titrated with 11.0 mmol L−1 of TTAB at 298.15 K, ΔfH2980 = −10.31 kJ per mol of injectant. By adding TTAB to NaSal solution, two fluorescence lifetimes of salicylate were observed solely after wormlike micelle being formed. The correspondent lifetime values of 4.0 ns and 7.2 ns are respectively associated with the free and associated species of salicylate. The new results demonstrated that wormlike micelles are the first aggregate formed when TTAB is added to salicylate. This aspect is relevant for understanding the mechanism of wormlike micelles formation.