2021
DOI: 10.1021/acs.langmuir.0c03606
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Effects of Salt-Induced Charge Screening on AOT Adsorption to the Planar and Nanoemulsion Oil–Water Interfaces

Abstract: Nanoemulsions, nanosized droplets of oil, are easily stabilized by interfacial electric fields from the adsorption of ionic surfactants. While mean-field theories can be used to describe the impact of these interfacial fields on droplet stability, the influence of these fields on the adsorption properties of ionic surfactants is not well-understood. In this work, we study the adsorption of the surfactant sodium dioctyl sulfosuccinate (AOT) at the nanoemulsion and planar oil–water interfaces and investigate how… Show more

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Cited by 19 publications
(21 citation statements)
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“…From the equilibrium constant, we can also determine the Gibbs free energy of adsorption Δ G = − RT ln K for SDS surfactants at the o/w interface, which is with −26 kJ/mol consistent with previous reports for nanoemulsions and extended o/w as well as air–water interfaces. We point out that one can also use a modified Langmuir model that additionally accounts for bulk depletion of the surface-active species. That approach has been indeed set forth by Eisenthal and co-workers and was used since then also by other groups. ,,, If we now select the modified Langmuir isotherm to quantify interface adsorption, we see that both models overlap very well (Figure ) and provide within the experimental scatter identical values for σ max and Δ G (see details in Table S2 of the SI).…”
Section: Resultsmentioning
confidence: 65%
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“…From the equilibrium constant, we can also determine the Gibbs free energy of adsorption Δ G = − RT ln K for SDS surfactants at the o/w interface, which is with −26 kJ/mol consistent with previous reports for nanoemulsions and extended o/w as well as air–water interfaces. We point out that one can also use a modified Langmuir model that additionally accounts for bulk depletion of the surface-active species. That approach has been indeed set forth by Eisenthal and co-workers and was used since then also by other groups. ,,, If we now select the modified Langmuir isotherm to quantify interface adsorption, we see that both models overlap very well (Figure ) and provide within the experimental scatter identical values for σ max and Δ G (see details in Table S2 of the SI).…”
Section: Resultsmentioning
confidence: 65%
“…At this point, we note that a qualitative analysis of ζ-potential from nanoemulsions requires more elaborate models , that take into account Marangoni stresses on the adsorbed surfactants. Further support for our result from SHS that the surface excess of curved interfaces approaches that of an extended interface when the particle radius is ≳180 nm comes from a recent work by Carpenter et al who have studied AOT stabilized nanoemulsions with a mean particle radius of about 180 nm or larger using sum-frequency scattering.…”
Section: Resultsmentioning
confidence: 79%
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“…Under these conditions, the ζ-potential remains constant albeit at a more negative value for all pHs tested above 5.5. We attribute the more negative ζ-potential value to increased carboxylate adsorption caused by the added counterions that reduce nearby repulsive headgroup interactions . Hence, from the constancy in the ζ-potential for the fixed ionic strength, we conclude that the decrease in ζ-potential above pH 9 when the counterion concentration was not fixed (Figure , top traces) is due to increased counterions from the added base reducing the repulsive forces between neighboring surfactants.…”
Section: Resultsmentioning
confidence: 84%
“…7−10,13−21 Besides, the undertaken problem also replicates the limiting situation of large oil emulsions possessing interfacial charge density due to absorbed ionic surfactant molecules along the surface of the nanoemulsions. 68 In a recent study, Carpenter et al 69 estimated the interfacial ζpotential of nanoemulsions obtained from measured electrophoretic mobility using Ohshima's approximation to Henry's function 70 applicable for the NPs with rigid surface. Thus, the present result will also pave the way for a refined evaluation of the interfacial charge properties of such nanoemulsions.…”
Section: Introductionmentioning
confidence: 99%