Formation and Morphology of Reverse Micelles Formed by Nonionic Surfactants in “Dry” Organic Solvents

Pérez, Sofía V.; Olea, Andrés F.; Gárate, M. Pilar

doi:10.2174/1568026614666140118222419

Cited by 12 publications

(6 citation statements)

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“…For polyoxyethylene nonyl phenol type surfactants in cyclohexane, aggregation numbers between 20 and 50 are reported . An aggregation number of 156 is reported for C 10 E 6 in n -heptane . Both studies, however, do not specify W and do not state clearly the overall surfactant concentration other than that these were above the critical micelle concentration.…”

Section: Resultsmentioning

confidence: 99%

“…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%

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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: Resultsmentioning

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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“…Important characteristics needed to understand a micellar system include the CMC, hydrodynamic radius ( R h ), and the aggregation number ( N agg ) of the micelles. The CMC is defined as the concentration at which the formation of micelles occurs and is associated with the abrupt transition for a number of physical properties of the system including surface tension, conductivity, and turbidity . A number of other methods are also well suited for the study of reverse micelles including fluorescence spectroscopy, small‐angle X‐ray scattering, conductivity, SLS/DLS, transmission electron microscopy, and transient current …”

Section: Resultsmentioning

confidence: 99%

Micellization and Adsorption to Carbon Black of Polyisobutylene‐Based Ionic Liquids

Holbrook

Storey

2020

Journal of Polymer Science

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Ionic liquid-terminated polyisobutylene (PIB-IL) dispersants suitable for stabilization of carbonaceous deposits found in automotive lubricating oils were derived by the quaternization of tertiary amines (1-methyl-imidazole, pyridine, and isoquinoline) with primary bromide-terminated PIB. Characterization of PIB intermediate and PIB-IL dispersants was carried out by nuclear magnetic resonance, gel-permeation chromatography, thermogravimetric analysis (TGA), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and differential scanning calorimetry. PIB-IL micellization in dodecane and characteristics thereof (hydrodynamic radius, aggregation number, and critical micelle concentration) were investigated by static (SLS) and dynamic light scattering; whereupon, the selfassociation of PIB-IL was found to be highly sensitive to anion hydrophobicity. Qualitative adsorption of PIB-IL onto carbon black was confirmed by Fourier transform infrared and TGA measurements. Using Langmuir adsorption studies, the affinity for and adsorption to carbon black of PIB-IL were characterized. PIB-IL adsorption onto carbon black occurred via cation-π interactions and was identified to be highly dependent on the molar volume of the cation and independent of the anion. From the parameters obtained by the Langmuir adsorption isotherms, the spatial arrangement of PIB-IL on the carbon black surface was elucidated, in which all adsorbed PIB-IL were determined to exist in the elongated brush regime.

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Formation and Morphology of Reverse Micelles Formed by Nonionic Surfactants in “Dry” Organic Solvents

Cited by 12 publications

References 0 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

Micellization and Adsorption to Carbon Black of Polyisobutylene‐Based Ionic Liquids

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