Structure of cobalt Aerosol-OT reversed micelles studied by small-angle scattering methods

Eastoe, Julian; Steytler, David C.; Robinson, Brian H.; Heenan, Richard K.; North, A.N.; Dore, John C.

doi:10.1039/ft9949002497

Cited by 41 publications

(65 citation statements)

References 18 publications

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“…In such systems the exchange of Na + with Co 2+ or Ni 2+ is known to drive a sphere-to-rod transition, promoting viscosity enhancements up to 40-fold at 10 wt. % inorganic solvents [Eastoe et al, 1992[Eastoe et al, , 1993[Eastoe et al, , 1994. Modeling of small-angle neutron scattering (SANS) data is consistent with occurrence of rigid, rather than flexible, micellar rods.…”

Section: Small Molecule Co 2 Thickenerssupporting

confidence: 58%

Development of Small Molecule CO2 Thickeners for EOR and Fracturing

Lee

Cummings

Dhuwe

et al. 2014

SPE Improved Oil Recovery Symposium

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The ideal carbon dioxide (CO 2 ) thickener would be an affordable, safe, water-insoluble additive that could dissolve in CO 2 at typical wellhead and reservoir conditions during CO 2 enhanced oil recovery (EOR) and elevate the viscosity of CO 2 to the same value as the oil. Further, the additive would not require heating or an organic co-solvent to achieve dissolution. A CO 2 thickener could be a transformative technology in that it would eliminate unfavorable mobility ratios during CO 2 EOR and reduce or eliminate the need for WAG. A detailed history of prior attempts to thicken CO 2 with either high molecular weight polymers or small associating compounds is presented. Our strategy for designing a novel small molecule CO 2 thickener is then detailed. Each thickener candidate contains a strongly CO 2 -philic segment (e.g. a very short polymer or oligomer of silicone oil or polyprolylene glycol), and one or more somewhat CO 2 -phobic functional groups that induces intermolecular interactions that can lead to the formation of viscosity-enhancing supramolecular structures in solution.

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Section: Small Molecule Co 2 Thickenerssupporting

confidence: 58%

Development of Small Molecule CO2 Thickeners for EOR and Fracturing

Lee

Cummings

Dhuwe

et al. 2014

SPE Improved Oil Recovery Symposium

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“…Measurements at similar molar ratios to the ones studied here have been carried out on related AOT microemulsions where the usual Na + counterion has been exchanged for a variety of monovalent and divalent cations [20,[31][32][33][34]. As in the present measurements, power-law, q −1 scattering has been used to infer elongated, rodlike droplets in many of these systems and the tendency to form cylindrical droplets has been correlated with the hydrated volume of the counterion [20,33].…”

Section: Analysis Of Scattering Resultsmentioning

confidence: 79%

“…In short, the data are consistent with droplets undergoing gradual cylinder-sphere transitions with increasing X and cylindrical rather than globular shapes being favored with increasing droplet concentration. Considered in a broader context, the results suggest that such shape changes, at least qualitatively, are an intrinsic property of the AOT molecule rather than being intimately connected to the choice of counterion [20,[31][32][33][34].…”

Section: Introductionmentioning

confidence: 92%

Variations in Structure Explain the Viscometric Behavior of AOT Microemulsions at Low Water/AOT Molar Ratios

Sharifi

Kudla

Oliveira

et al. 2011

Zeitschrift Für Physikalische Chemie

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The viscosity of AOT/water/decane water-in-oil microemulsions exhibits a well-known maximum as a function of water/AOT molar ratio, which is usually attributed to increased attractions among nearly spherical droplets. The maximum can be removed by adding salt or by changing the oil to CCl 4 . Systematic small-angle X-ray scattering (SAXS) measurements have been used to monitor the structure of the microemulsion droplets in the composition regime where the maximum appears. On increasing the droplet concentration, the scattering intensity is found to scale with the inverse of the wavevector, a behavior which is consistent with cylindrical structures. The inverse wavevector scaling is not observed when the molar ratio is changed, moving the system away from the value corresponding to the viscosity maximum. It is also not present in the scattering from systems containing enough added salt to essentially eliminate the viscosity maximum. An asymptotic analysis of the SAXS data, complemented by some quantitative modeling, is consistent with cylindrical growth of droplets as their concentration is increased. Such elongated structures are familiar from related AOT systems in which the sodium counterion has been exchanged for a divalent one. However, the results of this study suggest that the formation of non-spherical aggregates at low molar ratios is an intrinsic property of AOT.

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“…In systems of mixed surfactants and hydrotropes of the same charge the electrostatic repulsion diminishes interfacial co-adsorption. Elongated microemulsions were discovered by Petit [13] and Eastoe et al [14][15][16] who first observed cylindrical or ellipsoidal reverse microemulsions with the Aerosol-OT (AOT) anion coupled with Cobalt counterions (substituted for the normally found Sodium ion). This work was taken further to explore the effects of different metal counterions on AOT microemulsion morphology [14][15][16], and recently showing elongated self-assembly structures in supercritical CO2 with related surfactants [17].…”

Section: Introductionmentioning

confidence: 99%

Effects of small ionic amphiphilic additives on reverse microemulsion morphology

Hatzopoulos

James

Rogers

et al. 2014

Journal of Colloid and Interface Science

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms Effects of small ionic amphiphilic additives on reverse microemulsion morphology Research Highlights Cylindrical morphologies of reverse microemulsions induced by small molecule hydrotropes.  Ellipsoidal droplets of high aspect ratio in reverse AOT microemulsions are induced by short chain alkanoate additives.  A cylinder to sphere transition in reverse AOT microemulsions is seen with increasing water content. . Microemulsion domain structures were investigated by small-angle neutron scattering (SANS), and these data were fitted by structural models to yield information on the shapes (spheres, ellipsoids or cylinders) and sizes of the nanodroplets. Effects of small ionic amphiphilic additives on reverse microemulsion morphology FindingsUnder the conditions of study hydrotrope chemical structure has a significant effect on microemulsion structure: sodium cyclohexanoate does not induce the formation of cylindrical/ellipsoidal nanodroplets, whereas the aromatic analogue sodium benzoate does. Furthermore, the short chain sodium hexanoate does not cause anisotropic microemulsions, but the more hydrophobic longer chain heptanoate and octanoate analogues do induce sphere-to-ellipsoid transitions. This study shows that underlying microemulsion structures can be tuned by hydrotropes, and that the strength of the effect can be identified with hydrotrope hydrophobicity in terms of the bulk aqueous phase cac.

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Structure of cobalt Aerosol-OT reversed micelles studied by small-angle scattering methods

Cited by 41 publications

References 18 publications

Development of Small Molecule CO2 Thickeners for EOR and Fracturing

Development of Small Molecule CO2 Thickeners for EOR and Fracturing

Variations in Structure Explain the Viscometric Behavior of AOT Microemulsions at Low Water/AOT Molar Ratios

Effects of small ionic amphiphilic additives on reverse microemulsion morphology

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