Scattering studies of microemulsions in low-density alkanes

Eastoe, Julian; Young, William K.; Robinson, Brian H.; Steytler, David C.

doi:10.1039/ft9908602883

Cited by 108 publications

(123 citation statements)

References 12 publications

Supporting

Mentioning

114

Contrasting

Order By: Relevance

“…39 Full accounts of the scattering laws are given elsewhere [39][40][41][42][43] . For polydisperse spherical droplets at volume fraction , radius Ri, volume Vi, and coherent scattering length density ρp dispersed in a medium of ρm, the normalized SANS intensity I(Q) (cm -1 ) may be written as…”

Section: High-pressure Small-angle Neutron Scattering (Hp-sans) Measumentioning

confidence: 99%

“…Earlier papers reported Ah of AOT to be 155 Å 2 at a W/scCO2 52 but 75 Å 2 at the water/air 53 and 72 Å 2 at the water/alkane interface. 41 Although the values of radii c av in Fig. 3 are approximately half those seen for AOT W/alkane μEs, 10 this could be accounted for owing to the difference in interfacial packing and the determined Ah By using the intercept for lh and eq.…”

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

confidence: 99%

“…For AOT in a range of n-alkanes from propane to decane, a mean value of 72 Å 2 for Ah was reported. 41 The difference in Ah between W/CO2 and W/O μEs suggests that packing density of AOT type surfactants at water surface increases in CO2 as compared to typical hydrocarbon oil. Earlier papers reported Ah of AOT to be 155 Å 2 at a W/scCO2 52 but 75 Å 2 at the water/air 53 and 72 Å 2 at the water/alkane interface.…”

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

confidence: 99%

“…[19][20][21]40,41 The fitted parameters are the volume fraction , the core radius c av , polydispersity index / c av , and shell thickness ts; these were initially set at physically reasonable values, radii obtained by preliminary 44 and the estimated length of the chains (12.7 Å for n = 8, 7.5 Å for n = 4, and 4.9 Å for n = 2) 32 , respectively. The sequence of fitting parameters was a follows; firstly, at constant / c av and ts values, the other two parameters were adjusted to the experimental data, and then suitable / c av and ts were obtained by floating for the best fit ( to minimize sum of weighted squared residuals).…”

mentioning

confidence: 99%

See 3 more Smart Citations

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

et al. 2013

Self Cite

View full text Add to dashboard Cite

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.

show abstract

Section: High-pressure Small-angle Neutron Scattering (Hp-sans) Measumentioning

confidence: 99%

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

confidence: 99%

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

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

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

et al. 2013

Self Cite

View full text Add to dashboard Cite

show abstract

“…The headgroup area was calculated for both surfactant systems giving 133 ± 5 Å 2 for 6FS(EO)2 and ℎ = 108 ± 5 Å 2 for 4FS(EO)2, which is in good agreement with literature results, obtained in a similar fashion for fluorinated di-chain surfactant with comparable structures: ℎ = 128 ± 5 Å 2 for 8FS(EO)2, 7 and ℎ = 115 ± 5 Å 2 for di-HCF4, di-HCF6 and di-CF4. 29 On the other hand, for normal hydrocarbon AOT-stabilized microemulsions in a range of alkane solvents 30 , a mean value of 72 Å 2 has been reported for ℎ . The smaller ℎ value of hydrocarbon (H-carbon) surfactants at w/o interface suggests a higher packing density compared with the fluorocarbon (F-carbon) surfactants at w/c interface, which can be rationalized as an enhanced packing efficiency of F-carbon chains at the w/c interface 40,41 .…”

Section: Effect Of Surfactant Chain Lengthmentioning

confidence: 99%

Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering

Yan

Sagisaka

James

et al. 2014

Journal of Colloid and Interface Science

Self Cite

View full text Add to dashboard Cite

HypothesisThe formation, stability and structural properties of normal liquid phase microemulsions, stabilized by hydrocarbon surfactants, comprising water and hydrocarbon oils can be interpreted in terms of the film bending rigidity (energy) model. Here, this model is tested for unusual water-in-CO2 (w/c) microemulsions, formed at high pressure with supercritical CO2 (sc-CO2) as a solvent and fluorinated surfactants as stabilizers. Hence, it is possible to explore the generality of this model for other types of microemulsions. Experiments In this paper, a High pressure Small-Angle Neutron Scattering (HP-SANS) study on w/c microemulsions is described using contrast variation to highlight scattering from the stabilizing fluorinated surfactant films: these data show clear evidence for spherical core-shell structures for the microemulsion droplets. FindingsThe results extend understanding of w/c microemulsions since previous SANS studies are based only on scattering from water core droplets. Here, detailed structural parameters for the surfactant films, such as thickness and film bending energy, have been extracted from the core-shell SANS profiles revealed by controlled contrast variation. Furthermore, at reduced CO2 densities (~0.7 g cm -3 ), elongated cylindrical droplet structures have been observed, which are uncommon for CO2 microemulsions/emulsions. The implications of the presence of cylindrical micelles and droplets for applications of CO2, and viscosity enhancements are discussed.

show abstract

UV, EPR, X‐ray and Related Spectroscopic Techniques

Yonker¹,

Linehan²,

Fulton³

1999

Chemical Synthesis Using Supercritical Fluids

View full text Add to dashboard Cite

The techniques described in Chapters 3.1 and 3.2 provide information on a molecular level about solute structure, solution dynamics and chemistries in SCFs. The goal of this chapter is to briefly discuss other spectroscopic techniques applied to SCFs which can be used to determine solution structure or the effects of pressure and temperature on reactions in these solvent systems. An overview of this type, by its nature, can not be considered inclusive, but it is hoped to give future practitioners in the field a reasonable expectation of the type of molecular-level information that different spectroscopic techniques provide under SCF conditions. UV-VisUV-Vis spectroscopy of compounds dissolved in SCFs has been used to determine solvent structure [l-61, solute solubilities [7,8], solid matrix changes [9, lo], and reaction kinetics [ll-161. UV-Vis is often the spectroscopic technique of first choice because many solute molecules of interest have an observable absorption band which can be used for identification and quantitation.In the simplest UV-Vis SCF experiment a pressure vessel (stainless steel or other high pressure metal alloy) is fitted with an inlet (and an outlet) connection for high-pressure tubing and high pressure windows (quartz, sapphire, or diamond). The relative strength of the window materials is diamond > sapphire > quartz. The pressure limits of the cell design depend on the window material and the area of the unsupported window exposed to the fluid pressure. The typical UV cutoff wavelengths for these materials are: sapphire -1500A, quartz -2100 A, and diamond type I1 -2600 A. Many different cell designs have been reported in the literature. A typical high pressure cell design is shown in Figure 3.3-1. The pressure seal between the sapphire window and the cell body is made with a gold plated metal V-ring. The path length is typically 2.5 cm and the cell volume is 3-4 mL. The sapphire windows are 1 cm thick and 2.5 cm in diameter. Common, high-pressure UV-Vis spectroscopy

show abstract

Scattering studies of microemulsions in low-density alkanes

Cited by 108 publications

References 12 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

Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering

UV, EPR, X‐ray and Related Spectroscopic Techniques

Contact Info

Product

Resources

About

Scattering studies of microemulsions in low-density alkanes

Cited by 108 publications

References 12 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

Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering

UV, EPR, X‐ray and Related Spectroscopic Techniques

Contact Info

Product

Resources

About

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

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