Micellization of DTAB, TTAB, HTAB in Water-DMF Solution

The CMC of long chain Alkyltrimethylammonium Bromides homologous series, HTAB(CTAB), TTAB, DTAB have been determined by means of electrical conductivity and surface tension measurements as a function of DMF molefractions(XDMF=0.00~0.30) at various temperatures(25°C~50°C). Thermodynamic parameters evaluated from experimental CMC values indicate that: 1) The micelle formation of these quaternary ammonium salts are relatively indifferent to the temperature change. 2) DMF solvent effect is remarkably large; ie. when the solvent composition changes XDMF=0.00→0.150 at 30°C, the corresponding changes of micellization parameters are ∆Gmo= -4.21→-2.45 kcal/mole, ∆Hmo=-1.27→-1.82 kcal/mole, ∆Smo=9.7→2.08 cal/deg for HTAB, ∆Gmo=-3.37→-1. 97kcal/mole, ∆Hmo= -1.53→-3.12 kcal/mole, ∆Smo=6.07→-5.12cal/deg for TTAB, ∆Gmo=-2.50→-1. 35kcal/mole, ∆Hmo= -1.34→-3.17 kcal/mole, ∆Smo=3.84→- 6.00calf deg for DTAB. 3) As the chain length of cation monomer of the surfactant increases, the solvent effect on the micelle formation is increasingly observed; ie, when the solvent composition changes XDMF=0.00→0.150 at 25°C, the CMC value increases sixfold for DTAB, ninefold for TTAB, nineteenfold for HTAB. This ~hows the quaternary ammonium salts micelle formation is inhibited in the Water-DMF solution as a result of cooperatively reduced hydrophobic interaction as the DMF content is increased. The inhibitory effect of DMF can be explained due to the rigidified Water-DMF liquid structure which will lead to the critically reduced entropy contribution, the main driving force on the micelle formation