Phase behavior and size variation of AOT-based W/O microemulsions by substituting H+ for Na+ as the counterion

Takashina, Shiho; Yoshida, Mikio; Gotoh, Kuniaki; Oshitani, Jun

doi:10.1016/j.colsurfa.2008.04.030

Cited by 12 publications

(21 citation statements)

References 39 publications

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“…When H-AOT mole fraction grows, screening of the electrostatic repulsion between sulfonate groups by the counterion weakens, the distance between the polar headgroups increases, and the droplet size rises. Further increase in the proportion of H-AOT leads to destabilization of the interface of the microemulsion droplets [29]. The increase of electrostatic repulsion between the polar phosphate groups with DEHPA introduction can also take place in the instigated NaDEHP microemulsion.…”

Section: Droplet Sizementioning

confidence: 99%

Effect of Bis‐(2‐ethylhexyl)Phosphoric Acid on Sodium Bis‐(2‐ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non‐Ferrous Metals

Мурашова

Levchishin

Yurtov

2014

J Surfact & Detergents

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The effect of bis‐(2‐ethylhexyl)phosphoric acid (DEHPA) on the region of existence, conductivity and structure of sodium bis‐(2‐ethylhexyl)phosphate (NaDEHP) microemulsion has a dual nature and depends on DEHPA concentration. In the system NaDEHP–DEHPA–kerosene–water, the narrowing of the microemulsion region is observed with DEHPA concentration in the organic phase growth from 0.1 to 0.5 mol/L. The increase of DEHPA concentration in the organic phase from 0.1 to 0.4 mol/L leads to the reduction of electrical conductivity of the microemulsions. Based on the conductivity and viscosity measurements, we suppose the transition from reverse microemulsion with isolated droplets to percolate microemulsion at volume fraction of water 0.18 ( W=CH2O/CNaDEHP = 8). Droplet size of the microemulsions increases linearly with W growth. The rise of DEHPA concentration in the organic phase from 0.1 to 0.3 mol/L causes the growth of the coefficient at W in the equation d = kW + b from 0.038 to 0.249, i.e., it increases the slope of the lines. In contrast, DEHPA introduction at the concentration 0.1 mol/L (in the organic phase) leads to the expansion of the microemulsion region, does not affect the conductivity and decreases the coefficient at W. The rate of copper recovery into the microemulsion increases considerably with the rise of DEHPA concentration from 0.0 to 0.3 mol/L; no dual effect is observed. The following composition of the microemulsion for non‐ferrous metals leaching is recommended: CNaDEHP = 1.6 mol/L, CDEHPA = 0.3 mol/L (in the organic phase); W = 8–32.

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Section: Droplet Sizementioning

confidence: 99%

Effect of Bis‐(2‐ethylhexyl)Phosphoric Acid on Sodium Bis‐(2‐ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non‐Ferrous Metals

Мурашова

Levchishin

Yurtov

2014

J Surfact & Detergents

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“…26 We have investigated the screening effect of the counter ion. 7,8 There exists an electrostatic repulsion between the negatively charged AOT's polar headgroups, so the repulsion must be screened to a certain extent by the positively charged counter ion to form a stable interface. W/O microemulsion is not formed and phase separation occurs when pure water, H-AOT (hydrogen bis(2-ethylhexyl) sulfosuccinate), and isooctane are mixed, because the screening effect of H + is weaker than that of Na + .…”

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confidence: 99%

“…W/O microemulsion is not formed and phase separation occurs when pure water, H-AOT (hydrogen bis(2-ethylhexyl) sulfosuccinate), and isooctane are mixed, because the screening effect of H + is weaker than that of Na + . 7 The screening effect of alkali metal counter ions is in the order K + µ Rb + > Cs + > Na + > Li + , and the difference in the screening has an effect on H-AOTbased W/O microemulsion formation. 8 Here, instead of the counter ion, we focused on the screening effect of a surfactant that has a positively charged polar headgroup; C n -TAB (n = 8, 10, and 12; octyl-, decyl-, and dodecyltrimethylammonium bromide).…”

mentioning

confidence: 99%

“…H-AOT was prepared by ion exchange from Na-AOT, as described previously. 7 Pure water of 18.2 M³ cm was prepared using a Direct-Q System (Nihon Millipore). Preparations and measurements described below were carried out at 25°C.…”

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confidence: 99%

“…The size of a few thousand nanometers at the lower X Cn-TAB is not due to microemulsions but rather due to air bubbles produced during the emulsification. 7 At higher X Cn-TAB , I OH(water) , and I SO3 À increase from zero (the values for C 12 -TAB and C 10 -TAB reach approximately 1.0; some values are more than 1.0, because I OH(water) and I SO3 À are affected by the base line of FT-IR spectra), and the size is a few tens of nanometers; W/O microemulsion is formed. These results suggest that at the higher X Cn-TAB , the screening of electrostatic repulsion between the negatively charged AOT's polar headgroups by the positively charged C n -TAB's polar headgroups is sufficiently strong to form a W/O microemulsion.…”

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confidence: 99%

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Water-in-oil Microemulsion Formation with Aqueous Cn-TAB Solution and H-AOT/Isooctane Solution

et al. 2012

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Aqueous C n -TAB (n = 8, 10, and 12; octyl-, decyl-, and dodecyltrimethylammonium bromide) solution and isooctane solution of H-AOT (hydrogen bis(2-ethylhexyl) sulfosuccinate) were mixed using a vortex mixer to produce a water-in-oil (W/O) microemulsion. The microemulsion was formed with the critical amount of C n -TAB; the order of the critical amount was C 12 -TAB < C 10 -TAB < C 8 -TAB. A possible cause for the microemulsion formation was proposed based on the screening of the electrostatic repulsion between negatively charged AOT's polar headgroups by the positively charged C n -TAB's polar headgroups, the hydrophobic interaction between hydrocarbon chains, and hydrated water around AOT's polar headgroup.A water-in-oil (W/O) microemulsion is a thermodynamically stable dispersion of nanosized water droplets surrounded by surfactants in an oil phase. Na-AOT (sodium bis(2-ethylhexyl) sulfosuccinate), containing a sulfonate polar headgroup, two hydrophobic branched hydrocarbon chains with carbonyl groups, and a sodium counter ion, is widely used as a surfactant to form W/O microemulsions. The water content, temperature, nature of the oil phase, and surfactant concentration determine the W/O microemulsion properties.1 Counter ion is also an important determinant factor. 26 We have investigated the screening effect of the counter ion. 7,8 There exists an electrostatic repulsion between the negatively charged AOT's polar headgroups, so the repulsion must be screened to a certain extent by the positively charged counter ion to form a stable interface. W/O microemulsion is not formed and phase separation occurs when pure water, H-AOT (hydrogen bis(2-ethylhexyl) sulfosuccinate), and isooctane are mixed, because the screening effect of H + is weaker than that of Na + . 7 The screening effect of alkali metal counter ions is in the order K + µ Rb + > Cs + > Na + > Li + , and the difference in the screening has an effect on H-AOTbased W/O microemulsion formation. Here, instead of the counter ion, we focused on the screening effect of a surfactant that has a positively charged polar headgroup; C n -TAB (n = 8, 10, and 12; octyl-, decyl-, and dodecyltrimethylammonium bromide). Generally, a cosurfactant (additional surfactant) like a long-chain alcohol is used to enhance the stability of the microemulsion. However, to our knowledge, the role of the cosurfactant has not been studied based on the screening effect. In this study, we investigated if the H-AOT-based W/O microemulsion can be formed due to the screening effect of the C n -TAB's polar headgroup and if the difference in hydrocarbon chain length can affect the microemulsion formation.Reagents used were Na-AOT from Aldrich, C 8 -TAB and C 10 -TAB from Tokyo Chemical Industry, and C 12 -TAB from ACROS Organics. All reagents were used as received. H-AOT was prepared by ion exchange from Na-AOT, as described previously.7 Pure water of 18.2 M³ cm was prepared using a Direct-Q System (Nihon Millipore). Preparations and measurements described below were carried out at 25°C....

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Phase behavior and size variation of Na-AOT-based W/O microemulsions by increasing NaOH concentration in the water pool

Oshitani¹,

Takashina²,

Yoshida³

et al. 2009

Advanced Powder Technology

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Phase behavior and size variation of AOT-based W/O microemulsions by substituting H+ for Na+ as the counterion

Cited by 12 publications

References 39 publications

Effect of Bis‐(2‐ethylhexyl)Phosphoric Acid on Sodium Bis‐(2‐ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non‐Ferrous Metals

Effect of Bis‐(2‐ethylhexyl)Phosphoric Acid on Sodium Bis‐(2‐ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non‐Ferrous Metals

Water-in-oil Microemulsion Formation with Aqueous Cn-TAB Solution and H-AOT/Isooctane Solution

Phase behavior and size variation of Na-AOT-based W/O microemulsions by increasing NaOH concentration in the water pool

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