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The Influence of pH and Temperature on the Equilibrium and Dynamic Surface Tension of Aqueous Solutions of Sodium Oleate
2001 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 239, no 1, 209-216 p.Article in journal (Refereed) Published
Abstract [en]

For aqueous solutions of sodium oleate, the dynamic surface tension (using the maximum bubble pressure technique) and the equilibrium surface tensions (using the du Nouy ring method) were studied. Experiments were carried out within the pH range 7 to 13 and at temperatures from 20 to 60 degreesC. From the equilibrium surface tension studies at 25 degreesC, a wide variation in surface activity was found to occur in the premicellar concentration range, depending on pH and oleate concentration, and this was explained on the basis of the formation of strongly surface-active premicellar species. It was also shown that the critical micelle concentration (cmc) of the system increased with pH within the pH range 7-12, Dynamic surface tension experiments were carried out from 20 to 60 degreesC at concentrations beyond the cmc in alkaline solutions, and the adsorption kinetics at the air/solution interface were analyzed using established theoretical diffusion models. From these data, the effective diffusion coefficients (D-eff) for the oleate species were determined and the presence of an interfacial activation barrier in the diffusion process was confirmed. It was found that the D-eff values obtained within the temperature range from 40 to 60 degreesC at 2-3 mM were in general agreement with previously reported values for the oleate dimer obtained by pulse-gradient FT-NMR. Furthermore, D-eff significantly increased with temperature and also increased with concentration at higher temperatures (> 40 degreesC).

Place, publisher, year, edition, pages
2001. Vol. 239, no 1, 209-216 p.
Keyword [en]
dynamic surface tension, equilibrium surface tension, sodium oleate, diffusion coefficient
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-9037DOI: 10.1006/jcis.2000.7543ISI: 000169533100026OAI: oai:DiVA.org:kth-9037DiVA: diva2:14578
Note
QC 20100923Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Studies of surfactant behaviour and model surfaces relevant to flotation deinking
Open this publication in new window or tab >>Studies of surfactant behaviour and model surfaces relevant to flotation deinking
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The objective of this work was to investigate the behaviour of some model surfactants used in the deinking process, namely, sodium oleate and two ethoxylated nonionic surfactants (C12E6 and C14E6) as well as to investigate the suitability of various model substrates for mimicking interactions in technical systems. The influence of the adsorption to the air � water interface has been measured by means of equilibrium and dynamic surface tension measurements, as well as foaming experiments. It was found that the solution pH and temperature influenced the dynamic and equilibrium surface tensions and the value of the cmc. Equilibrium surface tension measurements were also performed with mixtures of sodium oleate and nonionic surfactants and a strong synergistic effect was obtained, which means that a greater surface tension reduction can be obtained at lower surfactant concentrations. The foaming experiments, carried out with a Foam Scan Apparatus, showed an approximately constant total foam volume for both the pure surfactant systems and for the mixtures. In addition, the foam was slightly more stable for the mixtures than for the pure components.

Friction and surface forces between solid surfaces in liquid were studied using the atomic force microscope (AFM) from which inferences about the adsorption to these interfaces could be drawn. The AFM measurements were performed with the colloidal probe technique using cellulose as colloidal probe and an alkyd resin as a model ink surface. Mica and silica were both used as models for hydrophilic surfaces. Adsorption was observed on the alkyd resin, both with sodium oleate and with C12E6. The adsorption was registered both as a change in normal surface force interaction and as a strong reduction in friction force and friction coefficient at increasing surfactant concentration. The magnitude of the friction force was observed to be dependent on the adhesion and varied monotonically with the surface roughness. Measurements of adhesion and friction forces in air were performed, and the same conclusions about the effect of roughness were drawn. Finally the friction force behaviour appears to be similar if the adhesion is caused by a vapour bridge in liquid, or by a liquid bridge in air, where the formation of a capillary bridge in air is strongly dependent on the relative humidity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 68 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0601
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-602 (URN)91-7178-259-1 (ISBN)
Public defence
2006-02-10, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2010-09-23Bibliographically approved

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