Study of the size and morphology of aggregates formed by pentaethylene glycol monooctyl ether (C8EO5) in n-heptane

Sandoval, Tania E.; Espinoza, Luis; Guerra, Ignacio; Olea, Andrés F.; Gárate, M. Pilar

doi:10.1016/j.colsurfa.2012.02.002

Cited by 6 publications

(8 citation statements)

References 12 publications

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“…The constant c in eq has been much studied and discussed to account for deviations from the simplifying assumptions of the Stokes–Einstein equation that the particle is considered as a sphere of an effective radius, r , moving through a homogeneous solvent medium consisting of solvent molecules of much smaller size than the solute. The value of c is typically between 4 and 6, depending on the slip boundary and stick boundary conditions. , Gárate and co-workers have explicitly evaluated ranges of possible sizes for prolate, oblate, and cylinder structures of C 8 E 4 , C 8 E 5 , and C 10 E 6 in n -heptane using the corresponding adjusted Stokes–Einstein equations. , However, they were neglecting the presence of unaggregated surfactant and used the viscosity of neat heptane instead of measuring the actual solution viscosity, which, as can be seen from Table S9, is significantly concentration dependent.…”

Section: Resultsmentioning

confidence: 99%

“…17,29 Gaŕate and co-workers have explicitly evaluated ranges of possible sizes for prolate, oblate, and cylinder structures of C 8 E 4 , C 8 E 5 , and C 10 E 6 in n-heptane using the corresponding adjusted Stokes−Einstein equations. 30,31 However, they were neglecting the presence of unaggregated surfactant and used the viscosity of neat heptane instead of measuring the actual solution viscosity, which, as can be seen from Table S9, is significantly concentration dependent.…”

Section: δ = T Kmmentioning

confidence: 99%

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Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Hoffmann

Bothe²,

Gutmann³

et al. 2018

J. Phys. Chem. B

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The colligative property freezing point depression is evaluated as a means for estimating the extent of aggregation for solutions of poly(ethylene oxide) alcohol (CE) nonionic surfactant in cyclohexane. Combined with additional measurements of self-diffusion coefficients, it is shown that both unaggregated CE as well as reverse micelles are significantly present for the entire range of measured CE concentration (0.048-2.35 mol kg). A change in speciation near 0.2 mol kg is indicated by the results from both freezing point depression and self-diffusion coefficient measurements. It is shown that average reverse micelle radii and aggregation numbers obtained from the ratio of solvent and CE self-diffusion coefficients are consistent with prior reported results. However, unreasonably small radii for the reverse micelles as well as for the cyclohexane were obtained from analysis of the results by the Stokes-Einstein equation using additional measured solution viscosities. The concentration of reverse micelles and unaggregated CE was calculated from the freezing point depression results using the aggregation numbers obtained from ratio of self-diffusion coefficients. These concentrations indicate that the reverse micelles become smaller in average size and increase in number with increasing temperature without an increase in unaggregated CE.

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Section: Resultsmentioning

confidence: 99%

Section: δ = T Kmmentioning

confidence: 99%

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Hoffmann

Bothe²,

Gutmann³

et al. 2018

J. Phys. Chem. B

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show abstract

“…Knowledge about the characteristics of the reverse micelle structure such as the average diameter and aggregation number (the number of surfactant molecules in a reverse micelle) is therefore desirable. One experimental approach that has been used to obtain such structural information of reverse micelles in nonpolar solvents is to measure the self-diffusion coefficient, D , using fluorescence correlation spectroscopy , or, as is the focus in this report, NMR spectroscopy. − In conjunction with the solution viscosity, η, taken either from literature of the pure solvent or more accurately measured directly for the micellar solutions, access to the desired average radius of the reverse micelle can principally be obtained through the well-known Stokes–Einstein equation where k B is the Boltzmann constant, T the temperature in Kelvin, and c is a constant. Some reported investigations were modifying the Stokes–Einstein equation to take into account the possible nonspherical shape of the reverse micelle. , However, we caution that details on micelle shape may not be accessible because of the long time scale of NMR measurements.…”

Section: Introductionmentioning

confidence: 99%

Breakdown of the Stokes–Einstein Equation for Solutions of Water in Oil Reverse Micelles

et al. 2020

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An experimental study is presented for the reverse micellar system of 15% by mass polydisperse hexaethylene glycol monodecylether (C10E6) in cyclohexane with varying amounts of added water up to 4% by mass. Measurements of viscosity and self-diffusion coefficients were taken as a function of temperature between 10 and 45 °C at varying sample water loads but fixed C10E6/cyclohexane composition. The results were used to inspect the validity of the Stokes–Einstein equation for this system. Unreasonably small reverse average micelle radii and aggregation numbers were obtained with the Stokes–Einstein equation, but reasonable values for these quantities were obtained using the ratio of surfactant-to-cyclohexane self-diffusion coefficients. While bulk viscosity increased with increasing water load, a concurrent expected decrease of self-diffusion coefficient was only observed for the surfactant and water but not for cyclohexane, which showed independence of water load. Moreover, a spread of self-diffusion coefficients was observed for the protons associated with the ethylene oxide repeat unit in samples with polydisperse C10E6 but not in a sample with monodisperse C10E6. These findings were interpreted by the presence of reverse micelle to reverse micelle hopping motions that with higher water load become increasingly selective toward C10E6 molecules with short ethylene oxide repeat units, while those with long ethylene oxide repeat units remain trapped within the reverse micelle because of the increased hydrogen bonding interactions with the water inside the growing core of the reverse micelle. Despite the observed breakdown of the Stokes–Einstein equation, the temperature dependence of the viscosities and self-diffusion coefficients was found to follow Arrhenius behavior over the investigated range of temperatures.

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“…It is therefore important to explore new and more environmentally friendly solvents. The literature shows more than a few alternatives that could replace perc, such as hydrocarbons [5][6][7], silicone oils and liquid carbon dioxide [8] that have been proposed as attractive and competitive alternatives to chlorinated compounds like perc [9,10]. In this work, we have chosen carbon dioxide due its numerous toxicological advantages, harmless to humans that are in contact with it, like dry-cleaning workers or dry-cleaning customers.…”

Section: Introductionmentioning

confidence: 97%

Effect of the ethoxy groups distribution on the phase behaviour of the binary systems carbon dioxide CO2 with industrial non-ionic surfactants (CiEOj)

Sandoval

Gárate

Scavia

et al. 2013

The Journal of Chemical Thermodynamics

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Study of the size and morphology of aggregates formed by pentaethylene glycol monooctyl ether (C8EO5) in n-heptane

Cited by 6 publications

References 12 publications

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

Breakdown of the Stokes–Einstein Equation for Solutions of Water in Oil Reverse Micelles

Effect of the ethoxy groups distribution on the phase behaviour of the binary systems carbon dioxide CO2 with industrial non-ionic surfactants (CiEOj)

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