Nonlinear Response of a Batch BZ Oscillator to the Addition of the Anionic Surfactant Sodium Dodecyl Sulfate

Abstract

The response of the Belousov-Zhabotinsy (BZ) system to the addition of increasing amounts of the anionic surfactant sodium dodecyl sulfate (SDS) was monitored at 25.0 °C in stirred batch conditions. The presence of SDS in the reaction mixture influences the oscillatory parameters, i.e., induction period and oscillation period, to an extent that depends on the surfactant concentration. The experimental results have shown that the induction period increases slightly on increasing surfactant concentration and, then, a further increase in the [SDS] leads to an enhancement while the oscillation period increases monotonously on increasing SDS concentration. It has been proposed that the response of the oscillatory BZ system to the addition of SDS is due to the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species. Indeed, explanations of the experimental results have been given on the basis of the role played by the micellar shape, which in turn dictates the hydrophobic nature. The suggested perturbation effects have been supported by performing viscosity measurements on the aqueous SDS solutions and by the spectrophotometric estimation of the binding constant of the bromine species to the micellar aggregates. This study has indirectly corroborated the existence of two kind of micelles and unambiguously revealed that the bromine species show a different affinity toward the spherical and rod-like micelles