Conductance, apparent molar volume and compressibility studies of cetyltrimethylammonium bromide in aqueous solution of leucine

Abstract

In the present studies, micellization behavior of cetyltrimethylammonium bromide, CTAB (cationic surfactant) has been studied in the aqueous solution, containing 0.001, 0.005, 0.01, 0.025, 0.05, 0.075 and 0.1M leucine as a solvent, using specific conductances (κ), densities (d) and velocities of sound (v), in the temperature range 25–40°C at an interval of 5°C. The cmc of CTAB was determined from the plots of specific conductance (κ) of CTAB in aqueous leucine solution. The cmc values of surfactant increase with increase in temperature but they decrease linearly with increase in the concentration of the leucine. By using cmc data various thermodynamic parameters have also been evaluated. The apparent molar volume (ϕv) and apparent molar adiabatic compressibility (ϕκ) have been computed using densities and velocities of sound data. The above calculated parameters were found to be sensitive towards the interactions prevailing in the leucine–CTAB–water systems. The analysis of the data is found to suggest that ϕv and ϕκ values in general are positive at all temperatures and increase with rise in temperature while decrease sharply to about 0.8mM [CTAB] at all concentrations of leucine. Thereafter, the decrease is almost linear. The cmc as determined from the fluorescence measurements indicating a transition point of I1/I3 plot which shows that the cmc lies at ≈0.8mM, the results of which are consistent with the other physico-chemical studies. A reasonably good qualitative correlation is found to exist with regard to CTAB–leucine interactions obtained from the different measurements.