Estimation of the aggregation number and core radius of microemulsions

Izquierdo, Carmen; Moyá, Marı́a Luisa; Usero, J.L.; Casado, Julio

doi:10.1007/bf00817593

Cited by 20 publications

(25 citation statements)

References 11 publications

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“…The calculated Nagg and CPP are shown as a function of W0 in Figure 4 with previous data for AOT/W/nheptane μEs 10 . As expected from typical behavior of W/O reversed micelle systems 54,55 , Nagg for these W/CO2 μEs increased with W0. For example, Nagg was close to 10 at W0=10, but it reached up to ~100…”

Section: Adsorption and Aggregation Properties Of The Double-chain Flsupporting

confidence: 79%

“…On 19 the other hand, Nagg values of the FC surfactants in scCO2 μEs were found to be quite small, one fifth to one sixth of those of AOT/W/n-heptane μEs. Even if compared with AOT in the other organic solvents (eg, Nagg = ~90 at W0 = 10 and ~290 at W0 = 20 in isooctane and cyclohexane 54,55 …”

Section: Adsorption and Aggregation Properties Of The Double-chain Flmentioning

confidence: 99%

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Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

et al. 2013

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High-pressure small-angle neutron scattering (HP-SANS) studies were conducted to investigate nanostructures and interfacial properties of water-in-supercritical CO2 (W/CO2) microemulsions with double-fluorocarbon-tail anionic surfactants, having different fluorocarbon chain lengths and linking groups (glutarate or succinate). At constant pressure and temperature, the microemulsion aqueous cores were found to swell with an increase in water-to-surfactant ratio, W0, until their solubilizing capacities were reached. Surfactants with fluorocarbon chain lengths of n = 4, 6, and 8 formed spherical reversed micelles in supercritical CO2 even at W0 over the solubilizing powers as determined by phase behavior studies, suggesting formation of Winsor-IV W/CO2 microemulsions and then Winsor-II W/CO2 microemulsions. On the other hand, a short C2 chain fluorocarbon surfactant analogue displayed a transition from Winsor-IV microemulsions to lamellar liquid crystals at W0 =25. Critical packing parameters and aggregation numbers were calculated by using area per head group, shell thickness, the core/shell radii determined from SANS data analysis: these parameters were used to help understand differences in aggregation behavior and solubilizing power in CO2. Increasing the microemulsion water loading led the critical packing parameter to decrease to ~1.3 and the aggregation number to increase to > 90. Although these parameters were comparable between glutarate and succinate surfactants with the same fluorocarbon chain, decreasing the fluorocarbon chain length n reduced the critical packing parameter. At the same time, reducing chain length to 2 reduced negative interfacial curvature, favoring planar structures, as demonstrated by generation of lamellar liquid crystal phases.

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Section: Adsorption and Aggregation Properties Of The Double-chain Flsupporting

confidence: 79%

Section: Adsorption and Aggregation Properties Of The Double-chain Flmentioning

confidence: 99%

Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

et al. 2013

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“…In all media studied, no dependence of V u was found with the surfactant concentration at fixed W. This result was expected, taking into account that an increase of the surfactant concentration only produces an increasing of the number of droplets in the reverse micellar system [31].…”

Section: Apparent Molar Volumesmentioning

confidence: 52%

Study of water solubilized in AOT/n-decane/water microemulsions

Valero¹,

Sánchez²,

Gómez-Herrera³

et al. 2008

Chemical Physics

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“…The spectra for a given w 0 for the two solvents are identical within experimental error, which supports previous experimental results that concluded that the micelle size varies little with the identity of the nonpolar solvent. 13 As has been discussed extensively previously, 12 the spectra exhibit a systematic blue shift as the size of the micelle decreases. Compared to the peak absorption of the OD stretch of HOD in bulk water that falls at 2509 cm −1 , the OD spectrum of water in the w 0 = 2 micelle has its peak absorption at 2565 cm −1 .…”

Section: Methodsmentioning

confidence: 80%

“…Furthermore, a variety of solvents, including isooctane, hexane, toluene, and carbon tetrachloride, may be used as the nonpolar phase without significantly changing the size or characteristics of the enclosed water pool. 13,14 In this paper, we will address whether changing the identity of the nonpolar phase affects the dynamics of the water pool, even though the static properties, such as size, remain the same.…”

Section: Introductionmentioning

confidence: 99%

Water dynamics in small reverse micelles in two solvents: Two-dimensional infrared vibrational echoes with two-dimensional background subtraction

Fenn¹,

Wong²,

Fayer³

2011

The Journal of Chemical Physics

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Water dynamics as reflected by the spectral diffusion of the water hydroxyl stretch were measured in w 0 = 2 (1.7 nm diameter) Aerosol-OT (AOT)/water reverse micelles in carbon tetrachloride and in isooctane solvents using ultrafast 2D IR vibrational echo spectroscopy. Orientational relaxation and population relaxation are observed for w 0 = 2, 4, and 7.5 in both solvents using IR pumpprobe measurements. It is found that the pump-probe observables are sensitive to w 0 , but not to the solvent. However, initial analysis of the vibrational echo data from the water nanopool in the reverse micelles in the isooctane solvent seems to yield different dynamics than the CCl 4 system in spite of the fact that the spectra, vibrational lifetimes, and orientational relaxation are the same in the two systems. It is found that there are beat patterns in the interferograms with isooctane as the solvent. The beats are observed from a signal generated by the AOT/isooctane system even when there is no water in the system. A beat subtraction data processing procedure does a reasonable job of removing the distortions in the isooctane data, showing that the reverse micelle dynamics are the same within experimental error regardless of whether isooctane or carbon tetrachloride is used as the organic phase. Two time scales are observed in the vibrational echo data, ∼1 and ∼10 ps. The slower component contains a significant amount of the total inhomogeneous broadening. Physical arguments indicate that there is a much slower component of spectral diffusion that is too slow to observe within the experimental window, which is limited by the OD stretch vibrational lifetime.

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Estimation of the aggregation number and core radius of microemulsions

Cited by 20 publications

References 11 publications

Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

Study of water solubilized in AOT/n-decane/water microemulsions

Water dynamics in small reverse micelles in two solvents: Two-dimensional infrared vibrational echoes with two-dimensional background subtraction

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Estimation of the aggregation number and core radius of microemulsions

Cited by 20 publications

References 11 publications

Nanostructures in Water-in-CO2 Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

Nanostructures in Water-in-CO2 Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

Study of water solubilized in AOT/n-decane/water microemulsions

Water dynamics in small reverse micelles in two solvents: Two-dimensional infrared vibrational echoes with two-dimensional background subtraction

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Product

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Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

Nanostructures in Water-in-CO₂ Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers