Abstract

The critical micelle concentration(CMC) of CTAB was determined with changes in absorbance at 202nm band of 4-biphenyl acetate(<TEX>$BPA^-$</TEX>). With <TEX>$BPA^-$</TEX> as a probe, the effect of temperature on CMC of CTAB has been observed between <TEX>$30^{\circ}C{\sim}70^{\circ}C$</TEX>. In this range of temperature the values of CMC are <TEX>$1.18{\times}10^{-4}{\sim}2.02{\times}10^{-4}M$</TEX>. The free energy(<TEX>${\Delta}G^{\circ}m$</TEX>) and enthalpy(<TEX>${\Delta}H^{\circ}m$</TEX>)for the micellization of CTAB was negative and the entropy(<TEX>${\Delta}S^{\circ}m$</TEX>) 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 <TEX>$300MHz\;H^1-NMR$</TEX> data. The change in chemical shift of proton in CTAB as well as those of the protons in <TEX>$BPA^-$</TEX> 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(<TEX>$BPA^-$</TEX>) indicate the formation of mixed micelle between CTAB and <TEX>$BPA^-$</TEX>. The changes in chemical shifts of methylene protons in CTAB, demonstrate the penetration of <TEX>$BPA^-$</TEX> into the palisade layer of the CTAB micelle.