Abstract

The critical micelle concentration(CMC) of CTAB was determined with changes in absorbance at 202nm band of 4-biphenyl acetate($BPA^-$). With $BPA^-$ as a probe, the effect of temperature on CMC of CTAB has been observed between $30^{\circ}C{\sim}70^{\circ}C$. In this range of temperature the values of CMC are $1.18{\times}10^{-4}{\sim}2.02{\times}10^{-4}M$. The free energy(${\Delta}G^{\circ}m$) and enthalpy(${\Delta}H^{\circ}m$)for the micellization of CTAB was negative and the entropy(${\Delta}S^{\circ}m$) was a large positive value. The micellization of CTAB is considered as a spontaneous process and to involve a phase transition. The orientational binding of 4-biphenyl acetate anion to the CTAB micelle interface has been studied with $300MHz\;H^1-NMR$ data. The change in chemical shift of proton in CTAB as well as those of the protons in $BPA^-$ have been investigated by increasing the mole fraction of the anion in the mixed solutions. The changes in chemical shift with increasing mole fraction of anion($BPA^-$) indicate the formation of mixed micelle between CTAB and $BPA^-$. The changes in chemical shifts of methylene protons in CTAB, demonstrate the penetration of $BPA^-$ into the palisade layer of the CTAB micelle.