Acid Autocatalysis and Front Propagation in Water-in-Oil Microemulsions

Abstract

Experimental results are presented of an acid autocatalytic reaction (the bromate-sulfite clock reaction) performed in water-in-oil (w/o) microemulsions with neutral (Triton X-100, TX) or cationic (CTAB) surfactants. The characteristics of the pH-sensitive reaction in the stirred system are found to depend on the molar ratio of water to surfactant (ω 0 ) and the nature of the surfactant. The well-stirred reaction (clock) time is faster in the TX w/o microemulsion and slower in the CTAB w/o microemulsion compared to the aqueous phase clock. The pH change is reduced in the TX system and the initial and final pH are shifted to higher values in the CTAB system. The unstirred water-in-oil microemulsions support propagating acid reaction fronts with speeds up to a factor of 10 lower than the aqueous phase fronts. The results are explained through consideration of the effect of the confinement of water in the nanosized droplets on rates and equilibria and assuming front propagation is driven by the diffusion of hydrated reverse micelles.

NMR and Molecular Dynamics Study of the Size, Shape, and Composition of Reverse Micelles in a Cetyltrimethylammonium Bromide (CTAB)/n-Hexane/Pentanol/Water Microemulsion

“…Using eq 9 and eq 10, R H can be determined. (10) Using the average values of a and c obtained from the MD simulation, giving p = 0.41, a value of f oblate = 1.068 is obtained and hence a R H value of 2.93 nm. By using this value for p and assuming that the volume of the spherical droplet (V = (4/3)πR H…”

Propagation Behaviors of an Acid Wavefront Through a Microchannel Junction

“…22 Depending on the substrate used, the pH of these acid waves can be designed to range from 3 to 8, which is several orders higher than that of the BZ reaction solution. 23,24 Furthermore, such acid waves can be produced by various substrates, such as chlorite-tetrathionate, 25−29 chloritethiosulfate, 30−32 chlorite-thiourea, 33 chlorate-sulfite, 34 bromatesulfite, 23 bromate-sulfuric acid, 35 iodate-arsenous acid, 36−38 and iodide-nitric acid. 39 Although the substrates and pH conditions are quite different in each case, BZ and acid wave propagations have similar characteristics when considered as reaction-diffusion systems.…”

“…Similar to the BZ wave, proton-producing redox reactions of oxyanions are known to be autocatalytic and to manifest propagating acid fronts . Depending on the substrate used, the pH of these acid waves can be designed to range from 3 to 8, which is several orders higher than that of the BZ reaction solution. , Furthermore, such acid waves can be produced by various substrates, such as chlorite-tetrathionate, − chlorite-thiosulfate, − chlorite-thiourea, chlorate-sulfite, bromate-sulfite, bromate-sulfuric acid, iodate-arsenous acid, − and iodide-nitric acid …”

Accelerated Dynamics in Active Media: From Turing Patterns to Sparkling Waves

“…These two subsystems represent single droplets (a small subpopulation with the same size in the case of Φ d ≪ Φ p, 3 to 4 nm) coexisting together with a large number of nanodroplet clusters, one order of magnitude greater (peak centered around 20–25 nm). Bearing in mind that autocatalytic rate constants depend on droplet size, clusters can be considered a chemical subpopulation slightly different than droplets. Moreover, conductivity measurements around the percolation transition show values 10 times greater than in the nanodroplets regime (Figure b), although still lower in comparison to those obtained for volume fractions at Φ d ≫ Φ p .…”