EFFECT OF SURFACTANT HEAD GROUPS ON THE EXTENT OF SOLUBILIZATION OF SUDAN I DYE

Abstract

An important property of micelles in aqueous solution is their ability to increase the solubility of water insoluble compounds. In this work, the solubilization of Sudan I dye was studied in micellar solutions of three surfactants, possessing the same hydrocarbon tail but different hydrophilic head groups, namely sodium dodecylsulphate (SDS), dodecyltrimethylammonium bromide (DTAB), and dodecyl pentaethyleneoxide (C12EO5). From the result of CMC, the CMC of C12EO5 is much lower than DTAB and SDS. The results showed that, irrespective of the surfactant type, the solubility of Sudan I dye increased linearly with increasing surfactant concentration, as a consequence of the association between the dye and the micelles. The solubilization power and values of micelle-water partition coefficient calculated and found that these values are higher for C12EO5 than DTAB and SDS. Solubilization at micellar surface as well as in hydrophobic core of micelles that increase the solubilization of dye in C12EO5 micellar solution and much lower value of CMC are responsible for high solubilization power of it. The enhanced solubility of dye in DTAB micellar solutions than SDS is a resultant of electrostatic interaction between the positively charged surfactant head group and the polar groups present in the dye structure. The anionic surfactant SDS presented the least solubilization power as a result of electrostatic repulsions between the dye and the anionic surfactant head groups. The free energy of solubilization is energetically favorable for C12EO5 than DTAB and SDS.