Physicochemical studies on microemulsions

Chakraborty, Indranil; Moulik, Satya P.

doi:10.1016/j.jcis.2005.03.080

Cited by 32 publications

(20 citation statements)

References 41 publications

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“…17 One is the static percolation model, which is also considered the bicontinuous structure, while the other is the dynamic percolation model considering the formation of clusters or transient fusion between RMs due to Brownian motion and allowing exchange of water and ions in RMs. In the case of static percolation, the exponents n and s are expected to be 1.9, 18 which is much larger than the values in the present study, suggesting the dynamic percolation.…”

Section: ¹1contrasting

confidence: 80%

Percolation Behavior of Nonionic Reverse Micellar Solution

Aramaki¹,

Ichikawa²,

Shrestha³

2017

Chem. Lett.

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We report the percolation behavior of nonionic surfactant reverse micelles (RMs) composed of sorbitan laurate (Span20) and poly(oxyethylene) sorbitan monooleate (Tween80) in isopropyl myristate (IPM) in presence of a trace amount of water and electrolyte (KCl). Abrupt increase of conductivity above 20°C for oil/surfactant = 8/2 and Span20/Tween80 = 3/2 composition is an indication of the typical percolation behavior. The dynamic percolation behavior was suggested based on the scaling analysis of the conductivity change around the percolation temperature. Contrary to the ionic surfactant RMs, conductivity maxima was observed in the present nonionic RM system. Small-angle X-ray scattering (SAXS) data showed sphere-to-rod-type RM microstructure transition with increasing temperature in the lower temperature region. On the other hand, RM shrunk in the high temperature region due to dehydration of poly(oxyethylene) chains. It is anticipated that this characteristic feature of nonionic surfactant led to the depercolation at high temperatures.Keywords: Reverse micelle | Percolation | Conductivity Self-assembly has been recognized as a ubiquitous aspect of modern chemistry. 13 Reverse micelle (RM) or w/o microemulsion formed in nonpolar solvents, which is one of the surfactant self-assembled structures, has not been as extensively studied as the normal micelles in aqueous systems, in spite of several promising applications such as reaction media for nanomaterial preparation, chemical and biological reactions. Among the RM studies, electrical percolation behavior in ionicsurfactant-based systems has been extensively studied.46 Although RMs in nonaqueous systems show limited conductivity at low temperature or at low water concentration, the conductivity abruptly increases after a threshold temperature or water content. It is generally believed that such electrical percolation occurs because of clustering or transient fusion of RMs,7,8 which allows transfer of ions in the water pool of RMs. Percolation behavior in ionic surfactant (especially Aerosol OT) RM systems has been broadly investigated over the decades. However, percolation in nonionic surfactant RMs have been sparsely studied. 9,10 We have extensively studied the shape, size, and internal structure of nonionic surfactant RMs in surfactant/ oil system for the last ten years. We have successfully underlined the fundamental understanding of the microstructure and morphology control of nonionic surfactant RMs. 1113 Based on a decade-long experience on RMs, we aimed to study electrical percolation behavior of nonionic surfactant RM systems.Nonionic surfactants used in the present study, poly(oxyethylene) sorbitan monooleate (Tween80) and sorbitan laurate (Span20), were purchased from Sigma-Aldrich Co., and Tokyo Chemical Industry (TCI) Co., respectively. We chose those surfactants because it has been reported that nonionic reverse micelles or microemulsions can be formed using those surfactants.14,15 Isopropyl myristate (IPM) and potassium chloride (KCl) were purchas...

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Section: ¹1contrasting

confidence: 80%

Percolation Behavior of Nonionic Reverse Micellar Solution

Aramaki¹,

Ichikawa²,

Shrestha³

2017

Chem. Lett.

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“…The structural parameters of the microemulsion droplets were estimated following a simplified model. [28][29][30][38][39][40] The droplets were assumed to be monodisperse and spherical, having a monomolecular film of amphiphile at the interface in their dispersion in oil. V d and A d are given by the relations and V d is related with V w , V s , and V a i in the form…”

Section: Resultsmentioning

confidence: 99%

“…Structural Parameters. The structural parameters of the microemulsion droplets were estimated following a simplified model. − ,− The droplets were assumed to be monodisperse and spherical, having a monomolecular film of amphiphile at the interface in their dispersion in oil. V d and A d are given by the relations and V d is related with V w , V s , and in the form The knowledge of from the dilution protocol discussed above helps to get according to the relation For the evaluation of V s , a relation equivalent to eq 25 has been used.…”

Section: Resultsmentioning

confidence: 99%

Physicochemical Studies on Cetylammonium Bromide and Its Modified (Mono-, Di-, and Trihydroxyethylated) Head Group Analogues. Their Micellization Characteristics in Water and Thermodynamic and Structural Aspects of Water-in-Oil Microemulsions Formed with Them along with n-Hexanol and Isooctane

Mitra

Chakraborty²,

Bhattacharya³

et al. 2006

J. Phys. Chem. B

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The micellization behavior of cetylammonium bromide and its mono-, di-, and trihydroxyethylated head group analogues and water/oil (w/o) microemulsion formation with them have been studied with detailed thermodynamic and structural considerations. The critical micellar concentration, micellar aggregation number, and behavior of the surfactants at the air/solution interface have been studied in detail. The results have been analyzed and discussed. The formation of the w/o microemulsion stabilized by the aforesaid surfactants in conjunction with the cosurfactant n-hexanol in isooctane has been investigated by the dilution method. The energetics of the transfer of cosurfactant from oil to the interface has been estimated. The structural parameters, namely, droplet dimension, droplet number, and population of surfactant and cosurfactant on the droplet surface, have also been estimated. The efficacy of the surfactants in respect to water dispersion in oil and cosurfactant concentration level at the oil/water interface has been worked out. Such microemulsions are prospective compartmentalized systems to assist enzyme activities. In this respect, the trihydroxyethylated head group analogue in the above series has been found to be a better performer for the preparation and stabilization of microemulsions that has correlated well with its performance than the others in the hydrolysis of p-nitrophenyl-n-hexanoate by the enzyme Chromobacterium viscosum lipase.

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“…It can be assumed that the conductance in demineralized water was mainly governed by the concentration of the charge carrying particles. However, conductivity is a dynamic property and studies of aromatic and aliphatic hydrocarbon microemulsions have previously shown a range of different volume percolation thresholds 32 . This critical concentration is therefore highly dependent on the specific microemulsion properties.…”

Section: Resultsmentioning

confidence: 99%