Differential absorbance measurements of amphiphilic hemicyanine dyes, solubilization study in anionic surfactant

The solubilization of trans-amphiphilic hemicyanine dyes by the micelles of an ionic surfactant was studied by differential spectroscopic method. The critical micelle concentration (CMC) of sodium dodecylbenzenesulfonate (SDB S) with and without hemicyanine dyes was determined by conductivity measure ments. The partition coefficient between the bulk water and micelles of SDB S, K-x, was calculated using both differential spectroscopic and conductanc e data at 25.0 degrees C. The standard free energy change of solubilization , Delta G(p)degrees, of these amphiphilic hemicyanine dyes was determined f rom the partition coefficient values. The linear dependence of the free ene rgy change on the length of dialkyl hydrocarbon chains of the dyes on solub ilization predicted the contribution of a methylene group to the free energ y change, i.e. - 1.091 kJ mol(-1). The increase in K-x values with the hydr ophobicity of the dyes indicated that the solubilization was controlled mai nly by the hydrophobic interaction between the dyes and the micelles. The i nteraction coefficient (theta) and relative solubility (S-t/S-o) of dyes wi thin the SDBS micelles has also been evaluated and discussed. (C) 2000 Else vier Science B.V. All rights reserved.