An Investigation of the Effect of Ionic Strength on Micellization Behaviors of a Cationic Surfactant

Abstract

The conductivity measurement of tetradecyltrimethylammonium bromide (TTAB) provides information about its micellization behaviors in the presence of salts NaNO₃ and Na₂SO₄ in aqueous solutions. The presence of NaNO₃ and Na₂SO₄ in aqueous solutions of TTAB greatly influences the critical micellization concentration (CMC) of TTAB at 298.15, 308.15, and 318.15 K temperatures. Precisely measured conductivity data were used to determine CMC, degree of counter-ion dissociation (a), free energy of micellization (DG_m°), enthalpy of micellization (DH_m°), and entropy of micellization (DS_m°) of the TTAB in aqueous solutions in the presence of inorganic salts. The ionic strength in solution due to the presence of NaNO₃ and Na₂SO₄ affects the micellization thermodynamics of the TTAB in salt-water solvent systems. The study provides valuable insights regarding the effect of ionic strength, hydrophobic interaction, enthalpy change, and entropy change on micellization behaviors of TTAB. The DG_m°and DH_m°of TTAB becomes more negative in the presence of both NaNO₃ and Na₂SO₄ in aqueous solution, whereas DS_m° found to be maximum in the presence of Na₂SO₄. An increase in temperature in the investigated range increases the CMC of the TTAB in salt-water solvent systems.