Spectroscopic and kinetic investigation of the interaction between crystal violet and sodium dodecylsulfate

The interaction between crystal violet (CV) and SDS has been kinetically and spectroscopically studied. Kinetic results are consistent with an ion-pair formation process. In the absence of surfactant, the CV absorption spectrum is decomposed in two sub-bands centred at 17 953 cm−1 (λ = 557 nm) and 16 807 cm−1 (λ = 595 nm). In the presence of SDS we observe the formation of two new sub-bands centred at 18 939 cm−1 (λ = 528 nm) and 16 000 cm−1 (λ = 625 nm). The addition of surfactant results in an increase of the area of these sub-bands until they reach a maximum value for [SDS] ≈ 1 × 10−3 M and, afterwards diminish. At [SDS] ≈ 8 × 10−3 M there are no significant changes related to SDS addition. This behaviour has been explained considering the formation of ionic pairs between dye and SDS monomers. At one SDS concentration, the premicellar aggregation results in a destruction of SDS−CV+ ionic pairs. Later, an increase of SDS concentration yields the micelle formation and the dye incorporation on the micellar surface.