Liquid membrane oscillators

A short review of the different approaches to the mechanism of oscillations of electric potential difference between aqueous phases of liquid membrane oscillators is presented. More attention is paid to the mechanisms of oscillations proposed in our laboratory. For systems with cationic surfactant and ethanol the sudden adsorption and desorption of surfactant molecules at the aqueous acceptor phase/liquid membrane phase interface reinforced by the continuous feeding by diffusion are responsible for the observed oscillations. Adsorption and desorption of both alcohol and surfactant at the same interface are responsible for the oscillations in case of the system with anionic surfactant and butanol. The mechanisms were confirmed by mathematical simulations. The dynamics of the systems investigated is chaotic as shown by the attractors obtained in two-dimensional phase space.

Liquid membranes can be used not only for metal separation and water purification but also in LMO, which might be used as models for investigation of processes appearing in biomembranes or for molecular recognition. Such application of LMO requires the detailed knowledge of the mechanism of oscillations of DEd/a . Different oscillation patterns are observed (Fig. 2) depending on the type of surfactant or organic solvent used in LMO. Also, several approaches to the mechanism of oscillations can be found in literature [4,6 Á 10,12]. In this article, a short review of the different approaches to the mechanism of oscillations of electric potential difference between aqueous phases is presented. More attention was paid to a new and most advanced approach to the oscillation mechanism based on the laws of chemical kinetics [7,8]. For LMO with cationic surfactant and ethanol in the donor phase, sudden adsorption and desorption of surfactant cations with Br( and Pi( at the aqueous acceptor phase/ liquid membrane phase interface reinforced by the continuous feeding by diffusion, are responsible for the observed oscillations. This observation is valid for both types of liquid membrane used (nitrobenzene and nitromethane). In the case of system with anionic surfactant and butanol, adsorption and desorption of both alcohol and surfactant at the m /a interface are responsible for oscillations. Systematic numerical simulations show that the proposed mechanisms for systems with ionic surfactant can account for a great variety of observed oscillation patterns. The dynamic behavior of LMO can be followed by the corresponding two-dimensional attractors, phase space portraits [5] or Gabor spectra [13]. For three types of LMO studied (Fig. 2a Á c) the appropriate attractors were constructed (Fig. 3a Á c). They have different shape and show chaotic behavior of these systems. This feature of LMO allows using them for taste substance recognition [5].