Autocatalysis in liquid/liquid surfactant transfer

Abstract

Equilibrium and transfer properties of two surfactants (a non-ionic one, Brij5, and a cationic one, CTAB) were studied in water/oil biphasic systems. Water/air surface tension measurements provide information on both the partition coefficient and also on the type of aggregates formed: classical micelles or swollen micelles (oil-inwater microemulsion). A clear correlation is established between the type of aggregates and the kinetics recorded during transfer of the surfactant from the organic to the aqueous phase. Indeed, an accelerating kinetics is obtained for every system leading to the formation of swollen micelles. This is the first example of autocatalytic dynamics observed in biphasic conditions for a non-reactive system. This non-linear behavior, correlated to the Critical Aggregation Concentration, confirms the contribution of an interface mediated pathway, known as the ''budding mechanism'', to the formation of microemulsion for both non-ionic and ionic surfactants.

Mass-Spring Model of a Self-Pulsating Drop

“…Whether the transfer from the aqueous solution to the oil drop is relevant to triggering the instability or sustaining the pulsations is still open. The partitioning of CTAB between the aqueous and CH 2 Cl 2 phases highly favors the organic liquid, but the time scale of the transfer , is longer than a few tens of seconds and, as a consequence, cannot be invoked to be of major importance in the reloading process between two pulsations, although it might be important during the induction period for reaching the instability conditions. The surfactant transfer may nevertheless play a crucial role in the pulsating regime because it is often accompanied by Marangoni-type instabilities.…”

“…The surfactant transfer may nevertheless play a crucial role in the pulsating regime because it is often accompanied by Marangoni-type instabilities. A great deal of work has been recently done on the onset and development of convective Marangoni instabilities due to solute transfer. − When a solute is transferred from the water phase to the oil phase, an orthogonal gradient of solute concentration appears at the interface, which may enhance a local, small (thermal or solutal) Marangoni convection . Both the convection flow and concentration gradient grow in time until the instability fades because of convection-induced solute homogenization.…”

Self-Organized Liquid Crystal Droplets as Phototunable Softmasks

“…In such a scenario, the droplet is found to be under continuous self-propelling motion on the water−surfactant bath while ejecting an array of 5CB droplets through the threephase contact line. 54 In fact, the recoiling motion due to the asymmetry in the droplet ejection from the noncircular threephase contact line decides the direction of the movement of the primary droplet lens. The propulsion is found to be as high as 10 body lengths per second, while the droplet size is progressively reduced with the continuous ejection of the secondary droplets.…”

Mechanism and Kinetic Model for Autocatalysis in Liquid–Liquid System: Oxidation of Dibutyl Sulfide with Aqueous Hydrogen Peroxide

“…On the basis of the three typical mechanisms in liquid–liquid system mentioned in the Introduction, − we believed that the solvent effect could be the most reasonable mechanism , for the autocatalytic phenomenon because of the strong polarity of DBSO . The solubility experiments of aqueous H 2 O 2 in pure DBS and DBSO were investigated, and the results were shown in Figure .…”

“…In this reaction, surfactant-like sodium caprylate aggregated into micelles which could largely increase the surface area to accelerate the reaction rate. On the basis of the “micellar autocatalysis”, analogous inverse micelles, vesicles mechanism, and corresponding kinetic model were reported. − (2) Solvent effect mechanism: the product acted as solvent that could dissolve reactant in another phase. , For the biphasic alkaline hydrolysis of aromatic esters, Chen et al . demonstrated that the hydrotropic salts yielded by the hydrolysis itself could accelerate the apparent reaction rate by enhancing the solubility of the hydrophobic ester in water.…”