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 (SDBS) with and without hemicyanine dyes was determined by conductivity measurements. The partition coefficient between the bulk water and micelles of SDBS, Kx, was calculated using both differential spectroscopic and conductance data at 25.0°C. The standard free energy change of solubilization, ΔG°p, of these amphiphilic hemicyanine dyes was determined from the partition coefficient values. The linear dependence of the free energy change on the length of dialkyl hydrocarbon chains of the dyes on solubilization predicted the contribution of a methylene group to the free energy change, i.e. −1.091 kJ mol−1. The increase in Kx values with the hydrophobicity of the dyes indicated that the solubilization was controlled mainly by the hydrophobic interaction between the dyes and the micelles. The interaction coefficient (θ) and relative solubility (St/So) of dyes within the SDBS micelles has also been evaluated and discussed.