Interaction of hemicyanine dyes with the micelles of sodium dodecylbenzenesulfonate

Abstract

The critical micelle concentration (CMC) of sodium dodecylbenzenesulfonate (SDBS) in the presence of small amount of dialkylamino stilbazolium butyl sulfonate ( R = CH3 - C~ll ) dyes was determined by conductivity method at 25°C. The CMC of SDBS decrease linearly with an increase in the concentration of added dye within their low concentration regions. The rate ofCMC decrease versus the concentration of each dye at limiting dilution, provide the slope -dCMC/dCa ( = - k ). Information concerning the solublization of dialkylamino stilbazolium butyl sulfonate dyes in an ionic surfactant (SDBS) was obtained from Hitachi Double-beam Model 220 UV-visible spectrophotometer at 25°C. TIle partition coefficient Kx , of additives (dyes) between the bulk water phase and the micellar phase of SDBS was determined at 25°C by differential spectroscopic method. The value ofKy. are: for dye 1, 13424; for dye 2, 17713; for dye 3, 20039; for dye 4, 48729 and for dy 5, 67 236. The t d d free energy change f solublization, AGo p , was also determined for above five dyes. The values of Kx and AGo p for all dyes were again determined by an improved method which incorporate both conductance and differential spectroscopic data The value of Kx with improved relationship are: for dye 1, 13426; for dye 2, 17872; for dye 3, 20402; for dye 4, 48319 and for dye 5, 669155. The free energy change per methylene group, i.e., AGo (CHi) was also calculated which is -1.091 kJ/mol or - 0.261 kcal/mol in aqueous micellar solution of SDBS at 25°C. The effect of micelle forming surfactant SDBS on the visible spectra of above dye was also reported. Incorporation of dye molecules in micelle shift the spectra towards higher wavlength and magnitude of the shift increase with increasing the hydrophobicity of dyes. The spectral shift of dyes also depends upon the nature of the surfactant head group, on this basis of inetraction of the five dyes with micelles of SDBS has also been discussed. The absorption spectra of all the dyes in aqueous solution was also studied. The maximwn wavelength ( AmllY. ) increase with increasing hydrophobicity of dye. The increase in Amax is more prominent from dye 1 to dye 2 and this change is comparable as we go from dye 2 to dye 5. This is due the fact that there is removal of one p-hydrogen with carbon atom from methyl group in dye 1, then their is simply extension of alkyl chain. The interaction coefficient ( e ) between dye and surfactant (SDBS) was also evaluated and discussed.