Surfactant Transfer through a Liquid Membrane:  Origin of Spontaneous Oscillations at the Membrane/Acceptor Phase Interface

Abstract

Instability due to surfactant redistribution in a liquid membrane system consisting of two solutions, namely source and acceptor, separated by a layer of immiscible liquid is studied theoretically and experimentally. The transfer of a surfactant from a source phase to an acceptor phase is often accompanied by spontaneous nonlinear oscillations of electrical potential and/or interfacial tension. The oscillations can be generated at each of the membrane interfaces. Here a mechanism of oscillation, which develops at the membrane/acceptor phase interface, is proposed on the basis of direct numerical simulation of the system evolution. Performed experimental studies confirm the theoretical results.

Quasi-elastic Laser Scattering for Measuring Inhomogeneous Interfacial Tension in Non-equilibrium Phenomena with Convective Flows

“…A considerable number of studies have examined oscillatory liquid-membrane systems with different chemical compositions and geometries. 7,8,[43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59] In all of the cases studied, the surfactants in the donor phase were considered to be dissolved in the membrane phase and to transfer into the acceptor phase, but the origin of the electric potential oscillations remains controversial. 43,46,47 One issue in previous studies, which has caused controversy, is that interfacial tension measurements at the donor/membrane and the membrane/acceptor interfaces have never been made simultaneously.…”

“…In this threephase system, the magnitude of the interfacial tension became much larger (~9 mN m -1 ) than that (~1 mN m -1 ) in systems involving picric acid. 7,45,50 A plastic tube with a V-shaped deformation was inserted in order to separate the aqueous phases, similarly to a previous study. 51,60 Figures 3(b), 3(c) and 3(d) show the simultaneously measured time course of the interfacial tensions at the donor/membrane and at the acceptor/ membrane interfaces and of the electric potential between two aqueous phases, respectively.…”

“…In non-equilibrium open systems involving surfaces or interfaces, macroscopic molecular transport is observed even in isothermal processes with the concomitant spontaneous and rhythmical formation of regular spatio-temporal patterns and the motion of objects curried in the fluid. Such systems, called dissipative dynamic systems, occur, for example, under macroscopic agitation, during the flip-motion of a liquid/liquid interface, [3][4][5][6][7][8] or when objects display various modes of motion. [9][10][11][12][13][14][15][16][17][18] The BelousovZhabotinsky (BZ) reaction, which generates chemical oscillations in a bulk material, also produces sophisticated spatio-temporal patterns in an unstirred system.…”

Spontaneous Oscillation Mechanism by Simultaneous Time-resolved Measurements of Interfacial Tensions of Both the Donor/Membrane and Membrane/Acceptor Phases

“…Considerable numbers of additional researchers have also reported oscillatory liquid membrane systems of varying compositions. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] In all cases, the surfactant in the donor phase is considered to be dissolved into the membrane phase and transferred to the acceptor phase. Conversely, the mechanism of the oscillatory behavior of liquid membranes has been the subject of controversy, and several mechanisms have been proposed.…”

Propagation and Synchronization of Potential Oscillations in Multiple Liquid Membrane Systems

“…[5][6][7][8][9][10][11][12] Further, the oscillations of the membrane potential or the current in three-phase liquid membrane systems have been investigated extensively. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] One of the typical liquid membrane systems is composed of an aqueous solution containing cetyltrimethylammonium chloride (CTACl) and alcohol, W1, a nitrobenzene solution containing picric acid (HPic), O, and a pure water phase, W2, 13,[15][16][17][18][19][20][23][24][25] where such a potential oscillation appeared with an amplitude of 0.3 to 0.4 V and a period of 1 min. The oscillation mechanism of this system was proposed by the present authors, 23 where the amplitude of potential oscillation was explained by the difference in the Gibbs energies for the transfer of Pic -and Cl -from O to W2, and the adsorption and desorption of the H + Pic -ion pair at the O/W2 interface were requisite for the oscillation.…”