Spectrophotometric investigation of the monomer–dimer process of C.I. Basic Blue 9 in aqueous polymer–surfactant system

The monomer–dimer process of C.I. Basic Blue in an aq. solution of the anionic surfactant, sodium dodecyl sulfate and the nonionic polymer, polyvinyl alcohol, was investigated spectrophotometrically. The effective dimerization constant of the dye (effKD) was determined in the presence of the surfactant and polymer, both individually and in combination, from a low ionic strength buffered aq solution; the value of effKD increased in the order: PVA < SDS < PVA–SDS < H2O. Aggregation of the dye in the polymer–surfactant system was exothermic and displayed large negative ΔHo and negative ΔSo values. Below the CAC, the presence of surfactant facilitated dye dimerization whereas > CAC the dye dissolved monomerically in the surfactant/polymer complex; the monomer–dimer process of the dye was influenced by hydrophobic interactions.