Microemulsion structure and its effect on electrochemical reactions

Mackay, Raymond A.; Myers, Stephanie A.; Bodalbhai, L.; Brajter-Toth, Anna

doi:10.1021/ac00209a023

Cited by 74 publications

(59 citation statements)

References 29 publications

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Section: Electrochemical Measurementssupporting

confidence: 72%

“…The oxidation potential of Fc in the ME is therefore more anodic than in acetonitrile (E o '= 0.415 V vs. standard calomel electrode, SCE) and in water (E o '= 0.163 V vs. SCE). 24 On the other hand, as expected, the voltammogram in the cathodic region is not altered by the presence of Fc.By comparing the diffusion coefficient values for Fc oxidation from the oil phase and for water from droplets in the ME, it is observed that D Fc is, respectively, 60 and 40 times higher than D w/o for ME containing, respectively, isoamyl and amyl alcohol. Considering that water droplets are surrounded by a film of nonpolar tails of dodecyl sulfate anions and amyl or isoamyl chains, 14 its diffusion through the continuous oil medium must be slower than the one for Fc molecules.…”

supporting

confidence: 72%

“…Electroanalytical techniques may provide valuable information concerning the structural evolution, interparticle interaction and transport data, 17,23,24 yet there are very few studies employing electroanalytical methods in ME of water in vegetable oils. In this sense a Pt disk ultramicroelectrode (ume), allows to carry out linear voltammetric 25 measurements in resistive media 26 as is the case in this study.…”

Section: Introductionmentioning

confidence: 99%

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Water in soybean oil microemulsions as medium for electrochemical measurements

Mendonça¹,

Bica²,

Piatnicki³

2003

J. Braz. Chem. Soc.

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Microemulsões de água em óleo de soja (w/o ME) foram preparadas com dodecil sulfato de sódio (SDS) como surfactante e com os álcoois amílico ou isoamílico, como co-surfactantes. A composição 40,0% de óleo, 43,2% de álcool, 10,8% de SDS e 6,0% de água, em massa, na razão 1:4 [SDS]: [álcool], apresentou a maior estabilidade termodinâmica. O tamanho das gotículas e seu coeficiente de difusão nas microemulsões, D w/o , foram determinados por medidas de espalhamento de luz dinâmico (DLS). As reações de oxidação de ferroceno (Fc) e de água, e a redução de ácido oleico foram observadas nas ME por voltametria em um ultramicroeletrodo (ume) de disco de Pt. Os valores de D w/o determinados a partir de medidas eletroquímicas são menores do que os calculados a partir daquelas por DLS. Isto indica que a oxidação da água requer a difusão para o eletrodo tanto das gotículas como das moléculas de água nelas contidas. Os resultados evidenciam a possibilidade de determinação de analitos em óleos vegetais por métodos eletroanalíticos.Microemulsions of water in soybean oil (w/o ME) were prepared with sodium dodecyl sulfate (SDS) as surfactant and amyl or isoamyl alcohol, as co-surfactants. Microemulsions containing 40.0% oil, 43.2% alcohol, 10.8% SDS and 6.0% water in weight, in the ratio 1:4 [SDS]: [alcohol] showed the highest thermodynamic stability. The aqueous droplet size and its diffusion coefficient D w/o in the ME were determined through dynamic light scattering (DLS). Voltammetric measurements in the ME at a Pt disk ultramicroelectrode (ume) evidenced the oxidation of both water and ferrocene (Fc), and the reduction of oleic acid. The D w/o values calculated from the limiting current being lower than the ones obtained from DLS indicate that water oxidation probably requires diffusion towards the electrode of both the droplets and the water molecules from inside the droplets. The results show that electroanalytical determinations can be carried out in w/o ME. Keywords: microemulsions, soybean oil, voltammetry, ferrocene, oleic acid IntroductionEquilibria in water-oil interfaces have been studied in order to quantify solvent extraction as well as charge transfer processes. In this sense new analytical methodologies such as slow extrusion of water into a nonaqueous phase (and vice-versa) through a capillary, 1 the use of micrometric electrodes 2-3 and of microemulsions 4,5 (ME) have been proposed recently. Besides a significant decrease in costs and toxicity due to the decrease in organic solvents consumption, 6-8 water in oil ME allow to carry out electrochemical measurements due to the enhanced electrical conductivity imparted to the system by the presence of water.Microemulsions are thermodynamically stable systems composed of water, oil and surfactant, and, in some cases, an alcohol can be added as co-surfactant. 9-12 Their behavior is similar to the one of polar organic solvents and, although apparently homogeneous under visual observation, ME are actually microheterogeneous (perhaps nanoheterogeneous would be a better...

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Section: Electrochemical Measurementssupporting

confidence: 72%

supporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Water in soybean oil microemulsions as medium for electrochemical measurements

Mendonça¹,

Bica²,

Piatnicki³

2003

J. Braz. Chem. Soc.

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“…Furthermore, a bicontinuous microstructure, such as a network of water tubes in an oil matrix, or a network of oil tubes in a water matrix, with hydrocarbon and water regions stretching over large distances, has been identified in the intermediate regions. [20,21] Conductivity is frequently used to investigate structure and structural changes in microemulsions; estimating a microstructure using conductivity measurements is based on percolation theory. The static percolation model, which attributes percolation to the appearance of a bicontinuous water structure, has been proposed to describe the mechanism of percolation in traditional microemulsions.…”

Section: Microregions Of the Il Microemulsionmentioning

confidence: 99%

Structural Studies of 1‐Butyl‐3‐methylimidazolium Tetrafluoroborate/TX‐100/ p‐Xylene Ionic Liquid Microemulsions

Gao¹,

Zhang²,

Xu³

et al. 2006

ChemPhysChem

168

135

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The ionic liquid (IL) 1‐butyl‐3‐methylimidazolium tetrafluoroborate (bmimBF4) forms nonaqueous microemulsions with p‐xylene, with the aid of the nonionic surfactant TX‐100. The phase behavior of the ternary system is investigated, and three microregions of the microemulsions—ionic liquid‐in‐oil (IL/O), bicontinuous, and oil‐in‐ionic liquid (O/IL)—are identified by conductivity measurements, according to percolation theory. On the basis of a phase diagram, a series of IL/O microemulsions are chosen and characterized by dynamic light scattering (DLS). The size of aggregates increases on increasing the amount of added polar component (bmimBF4), which is a similar phenomenon to that observed for typical water‐in‐oil (W/O) microemulsions, suggesting the formation of IL/O microemulsions. The microstructural characteristics of the microemulsions are investigated by FTIR and 1H NMR spectroscopy. The results indicate that the interaction between the electronegative oxygen atoms of the oxyethylene (OE) units in TX‐100 and the electropositive imidazolium ring may be the driving force for the solubilization of bmimBF4 into the core of the TX‐100 aggregates. In addition, the micropolarity of the microemulsions is investigated by using methyl orange (MO) as a UV/Vis spectroscopic probe. A relatively constant polarity of the microemulsion droplets is obtained in the IL microemulsion. Finally, a plausible structure for the IL/O microemulsion is presented.

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“…[1][2][3] However, the application of these techniques in nanoheterogeneous systems, including microemulsions (MEs), has been scarcely exploited. MEs are optically transparent, isotropic and thermodynamically stable systems.…”

Section: Introductionmentioning

confidence: 99%

Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Mendonça¹,

Bica²,

Simó‐Alfonso³

et al. 2008

J. Braz. Chem. Soc.

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Microemulsões de água em óleo (ME w/o) constituídas de água, óleo de soja, SDS (dodecil sulfato de sódio) e diversos álcoois de cadeia curta foram caracterizadas sob o ponto de vista físico-químico e de propriedades eletroanalíticas. Foram testados diferentes co-surfactantes e razões surfactante:cosurfactante, sendo a ME com a composição mais favorável utilizada para estudar a cinética de processos redox. Para tanto, realizaram-se medidas de voltametria cíclica utilizando como eletrodo de trabalho um ultramicroeletrodo de disco de Pt e, como eletrodo de referência e auxiliar, foram usados Ag/AgCl e Pt, respectivamente, e ferroceno como uma sonda. Verificou-se que a estabilidade termodinâmica das MEs aumenta com o conteúdo de co-surfactante. A estrutura molecular e a solubilidade em água do co-surfactante afetam a condutividade elétrica e o raio hidrodinâmico das MEs. Devido aos baixos coeficientes de difusão observados na ME, foi possível a realização de medidas em estado transiente usando velocidades de varredura convencionais. A oxidação do ferroceno na ME demonstrou ocorrer em condições de quasi-reversibilidade. Assim, foi demonstrada a possibilidade de realizar estudos por voltametria cíclica em óleos vegetais sob a forma de ME w/o.Water/oil microemulsions (w/o ME) constituted by water, soybean oil, SDS (sodium dodecyl sulfate) and several short-chain alcohols were characterized from the viewpoint of its physical-chemical and electroanalytical properties. Different co-surfactants and surfactant:co-surfactant ratios were used, and the ME with the most favourable composition was used to study the kinetics of redox processes. For this purpose, cyclic voltammetry measurements using a Pt disk working ultramicroelectrode, an Ag/AgCl reference electrode and a Pt auxiliary electrode, and ferrocene as a probe, were performed. It was verified that the thermodynamic stability of the MEs increases with the co-surfactant content. The molecular structure and water solubility of the co-surfactant affect the electrical conductivity and the hydrodynamic radio of the MEs. Owing to the low diffusion coefficients verified in the MEs, measurements in transient state using conventional sweeping rates could be performed. Ferrocene oxidation in the ME has been demonstrated to proceed in quasi-reversibility conditions. Thus, the possibility of carrying out studies of cyclic voltammetry in vegetable oils under the w/o ME form was demonstrated.Keywords: w/o microemulsions, physical chemical properties, redox process, cyclic voltammetry, vegetable oils IntroductionValuable information relative to structure evolution, inter-particle interactions and transport data of mass and charge in diverse media, can be obtained by using electrochemical techniques. 1-3 However, the application of these techniques in nanoheterogeneous systems, including microemulsions (MEs), has been scarcely exploited. MEs are optically transparent, isotropic and thermodynamically stable systems. Water in oil (w/o) MEs are formed by water droplets dispersed in an oi...

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Microemulsion structure and its effect on electrochemical reactions

Cited by 74 publications

References 29 publications

Water in soybean oil microemulsions as medium for electrochemical measurements

Water in soybean oil microemulsions as medium for electrochemical measurements

Structural Studies of 1‐Butyl‐3‐methylimidazolium Tetrafluoroborate/TX‐100/ p‐Xylene Ionic Liquid Microemulsions

Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

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