Surface Composition Studies on (<i>n</i>-Hexane + Perfluoro-<i>n</i>-hexane) by Specular Neutron Reflection

Bowers, James; McLure, Ian A.; Whitfield, Richard; Burgess, A. N.; Eaglesham, A.

doi:10.1021/la950611i

Cited by 7 publications

(10 citation statements)

References 8 publications

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“…Such a problem is much rarer with fluorosurfactants that are not known to mix well with anything else mitigating mixing at the interface. [33][34][35][36] Having a low equilibrium surface tension is a necessary, but not sufficient, reason for the ability of a material to aid in flow and leveling. Rather it is the dynamic surface tension in the form of viscoelastic moduli, Gibbs elasticities, and diffusion coefficient that are perhaps better indicators of the ability of a material to function as a flow and leveling agent.…”

Section: Resultsmentioning

confidence: 99%

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Kausch¹,

Kim²,

Russell³

et al. 2003

Langmuir

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Interfacial rheological studies were performed on a series of bolaamphiphilic R,ω-(diammonium disulfato)-poly(fluorooxetane)s of several perfluoroalkyl chain lengths. Similar measurements were performed on a small-molecule, anionic fluorosurfactant with a -C8F17 perfluoroalkyl group that is known to be an effective flow and leveling aid in aqueous coatings. Dilational viscoelasticities were measured for the fluorosurfactants as a function of concentration and oscillation rate. Elasticities were found to increase with increasing perfluoroalkyl chain length. All elasticities exhibited a strain rate dependence indicative of the influence of diffusional relaxation on elasticity values. Phase angles were found to be in the range for diffusional relaxation and decreased with increasing concentration and strain rate. Using interfacial rheological data, characteristic fluid dynamics numbers were calculated for the fluorosurfactants. Among these was the Marangoni number. Calculated Marangoni numbers for the poly(fluorooxetane)s were of the same order of magnitude as that for the small-molecule, long perfluoroalkyl chain surfactant. The poly(fluorooxetane)s all have equilibrium surface tensions greater than that of the small-molecule, long perfluoroalkyl chain surfactant, yet show similar abilities to aid in flow and leveling in aqueous coatings at comparable concentrations. Rheological measurements demonstrate that equilibrium surface tension alone is not enough to explain the fluid dynamics processes occurring during flow and leveling.

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Section: Resultsmentioning

confidence: 99%

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Kausch¹,

Kim²,

Russell³

et al. 2003

Langmuir

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“…Several mixtures of alkanes (C 5 -C 8 ) and perfluoroalkanes (C 6 -C 8 ) have been examined at one or two temperatures, as well as a small number of mixtures involving other types of substances (alkylated polysiloxanes and perfluorotributylamine). McLure and co-workers [120,121] have performed neutron reflection experiments on the n-hexane + perfluoro-n-hexane mixture, supporting the view that a monolayer of the fluorinated component forms at the vapour-liquid interface for a range of temperatures both above and below the upper critical solution temperature (UCST). In all cases, the composition dependence of the surface tension exhibits large negative deviations from linear behaviour (reflecting the preferential adsorption of the less dense perfluoroalkane).…”

Section: Figure  Critical Temperatures T C Of Linear Alkanes []mentioning

confidence: 87%

SAFT-γ force field for the simulation of molecular fluids: 8. Hetero-segmented coarse-grained models of perfluoroalkylalkanes assessed with new vapour–liquid interfacial tension data

et al. 2016

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The air-liquid interfacial behaviour of linear perfluoroalkylalkanes (PFAAs) is reported through a combined experimental and computer simulation study. The surface tensions of seven liquid PFAAs (perfluorobutylethane, F 4 H 2 ; perfluorobutylpentane, F 4 H 5 ; perfluorobutylhexane, F 4 H 6 , perfluorobutyloctane, F 4 H 8 ; perfluorohexylethane, F 6 H 2 ; perfluorohexylhexane, F 6 H 6 ; and perfluorohexyloctane, F 6 H 8 ) are experimentally determined over a wide temperature range (276-350 K). The corresponding surface thermodynamic properties and the critical temperatures of the studied compounds are estimated from the temperature dependence of the surface tension. Experimental density and vapour pressure data are employed to parameterize a generic heteronuclear coarse-grained intermolecular potential of the SAFT-γ family for PFAAs. The resulting force field is used in direct molecular-dynamics simulations to predict the experimental tensions with quantitative agreement and to explore the conformations of the molecules in the interfacial region revealing a preferential alignment of the PFAA molecules towards the interface and an enrichment of the perfluoro groups at the outer interface region.

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“…The nature of its adsorption at the free liquid and silicaceous interfaces has been studied previously. 14,16,17 The hexane-h 14 ϩperfluorohexane mixtures are complemented, where appropriate, by isotopically related mixtures incorporating perdeutero-n-hexane ͑hexane-d 14 ). Hexane ͑Aldrich, 99 ϩ%͒, hexane-d 14 ͑Goss Scientific Ltd., 99ϩD at.…”

Section: A Choice Of System and Preparation Of Liquid Mixturesmentioning

confidence: 99%

“…Without recourse to deuterium labeling of the octadecyl chain, we are unable to establish the coverage of the coupled layer. As far as we can tell from the sensitivity of the measurements, the layer does not allow ingress of perfluorohexane when perfluorohexane is the subphase yet it contains ϳ15%-20% hexane when hexane-d 14 is the subphase. The fact that hexane but not perfluorohexane is taken up by the fluorophobic film may be attributable to the molecular size difference between hexane and perfluorohexane, the weakness of the A-PFA interaction, or, as we comment on shortly, the nature of the coupled film.…”

Section: A Characterization Of the Surfacesmentioning

confidence: 99%

Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. I. Nature of the noncritical adsorption profiles

Bowers

Zarbakhsh

Christenson

et al. 2003

The Journal of Chemical Physics

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Local structure of a phase-separating binary mixture in a mesoporous glass matrix studied by small-angle neutron scattering Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. II. Crossover from critical adsorption to complete wetting Neutron reflection has been applied to probe the nature and extent of adsorption from a mixture of (1Ϫx)n-hexaneϩx perfluoro-n-hexane against silicon substrates modified with alkylsilane ͑fluorophobic͒ or fluoroalkylsilane ͑fluorophilic͒ coupled layers. For an equimolar mixture (x ϭ0.5, 60.7 vol %͒ in the one-phase region at Tϭ30°C-removed both in temperature and composition from the upper critical point at 22.65°C and xϭ0.36-the structure was resolved at both fluorophobic and fluorophilic surfaces. Liquid mixtures with three different refractive index contrasts were used to reduce model ambiguity in the ensuing analysis. For both surfaces the composition profiles of the adsorbed liquids could be represented using two-layer slab models which included interlayer Gaussian roughness. For the fluorophobic surface, the thickness of the layer closest to the substrate is ϳ20 Å and composed of ϳ83 vol % n-hexane, and the second, more dilute layer has a composition profile which decays smoothly into the bulk over a range of ϳ100 Å. A similar result is found for the fluorophilic surface, but in this case the layer closest to the substrate is ϳ15 Å thick and composed of ϳ95 vol % perfluoro-n-hexane. Qualitatively similar behavior is found for adsorption from a mixture with xϭ0.7 against a fluorophobic substrate and for a mixture with xϭ0.2 against a fluorophilic substrate.

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Surface Composition Studies on (n-Hexane + Perfluoro-n-hexane) by Specular Neutron Reflection

Cited by 7 publications

References 8 publications

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

Interfacial Rheological Properties of a Series of Bolaamphiphilic Poly(fluorooxetane)s

SAFT-γ force field for the simulation of molecular fluids: 8. Hetero-segmented coarse-grained models of perfluoroalkylalkanes assessed with new vapour–liquid interfacial tension data

Adsorption from alkane+perfluoroalkane mixtures at fluorophobic and fluorophilic surfaces. I. Nature of the noncritical adsorption profiles

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