Energetic, surface-chemical and hydrodynamic studies on cetyltrimethylammonium bromide and sodium salicylate

Molecular interaction between cetyltrimethylammonium bromide (CTAB) and sod ium salicylate (NaSal) has been investigated. A 1:1 complex is formed in so lution. The mixed solution at this composition micellizes at 0.12 mmol.dm(- 3) at 30 degrees C, and the mixed micelle binds nearly 55% counter-ions. Th e molecular complex formation between CTAB and NaSal combination is an exot hermic process; The micellization of CTAB-NaSal combination is also exother mic and a two-step process, the overall enthalpy values falling in the rang e of 10-15 kJ mol(-1) at 30 degrees C. The micellization process is promine ntly entropy controlled. The surface excess of CTAB and its minimum area at the air-water interface in NaSal, NaCl and NaBr environments have been det ermined. The CTAB-NaSal system is non-Newtonian and viscoelastic, and show shear thinning properties.