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Interactions in Mixed Micellar Systems of an Amphoteric Chelating Surfactant and Ionic Surfactants
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.ORCID iD: 0000-0003-3407-7973
Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
2014 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 5, 1250-1256 p.Article in journal (Refereed) Published
Abstract [en]

Mixtures of ionic surfactants and the chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of interactions in mixed micellar systems. The amphoteric 4-C12-DTPA is zwitterionic with a negative net charge at the studied pH levels. The investigated ionic surfactants were the cationic dodecyltrimethylammonium chloride (DoTAC), the anionic sodium dodecyl sulfate (SDS), and the zwitterionic dimethyldodecylamine-N-oxide (DDAO). The surfactants all have the same hydrophobic chain lengths, and the results are evaluated in terms of headgroup interactions. 4-C12-DTPA interacts with different ionic surfactants by accepting or donating protons to the aqueous solution to increase the attractive interactions between the two surfactants; i.e., the protonation equilibrium of 4-C12-DTPA is shifted in different directions depending on whether there are predominant repulsions between positively or negatively charged groups in the mixed micelles. This was monitored by measuring pH vs concentration in the mixed systems. By measuring the pH, it was also possible to study the shift in the protonation equilibrium at increasing concentration, as the composition in the micelles approaches the composition in the total solution. Following the approach of Rubingh's regular solution theory, the interaction parameter β for mixed micelle formation was calculated from the cmc values determined by NMR diffusometry. Synergism in mixed micelle formation and negative β parameters were found in all of the investigated systems. As expected, the most negative β parameter was found in the mixture with DoTAC, followed by DDAO and SDS. The self-diffusion in the 4-C12-DTPA/DoTAC system was also discussed. The self-diffusion coefficient vs concentration plots show two distinctly different curves, depending on the surfactant that is present in excess.

Place, publisher, year, edition, pages
2014. Vol. 30, no 5, 1250-1256 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:miun:diva-21404DOI: 10.1021/la404656bISI: 000331344000008Scopus ID: 2-s2.0-84894189855OAI: oai:DiVA.org:miun-21404DiVA: diva2:698038
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2014-12-11Bibliographically approved
In thesis
1. Fundamental Characterization and Technical Aspects of a Chelating Surfactant
Open this publication in new window or tab >>Fundamental Characterization and Technical Aspects of a Chelating Surfactant
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The purpose of this study was to investigate the fundamental characteristics of a chelating surfactant in terms of solution behaviour, chelation of divalent metal ions, and interaction in mixtures with different foaming agents and divalent metal ion, as well as examining its prospects in some practical applications. Chelating surfactants are functional molecules, with both surface active and chelating properties, which are water soluble and therefore suitable for chelation in many aqueous environments. The dual functionality offers the possibility to recover the chelating surfactant as well as the metals.

The DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 4-C12-DTPA (2-dodecyldiethylenetriaminepentaacetic acid) was synthesized at Mid Sweden University. In the absence of metal ions, all eight donor atoms in the headgroup of 4-C12-DTPA are titrating and the headgroup charge can be tuned from +3 to -5 by altering the pH. The solution properties, studied by surface tension measurements and NMR diffusometry, were consequently found strongly pH dependent. pH measurements of chelating surfactant solutions as a function of concentration was used to extract information regarding the interaction between surfactants in the aggregation process.

Small differences in the conditional stability constants (log K) between coordination complexes of DTPA and 4-C12-DTPA, determined by competition measurements utilizing electrospray ionization mass spectrometry (ESI-MS), indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. This was further confirmed in hydrogen peroxide bleaching of thermomechanical pulp (TMP) treated with 4-C12-DTPA.

Interaction parameters for mixed systems of 4-C12-DTPA and different foaming agents were calculated following the approach of Rubingh’s regular solution theory. The mixtures were also examined with addition of divalent metal ions in equimolar ratio to the chelating surfactant. Strong correlation was found between the interaction parameter and the phase transfer efficiency of Ni2+ ions during flotations. Furthermore, a significant difference in log K between different metal complexes with 4-C12-DTPA enabled selective recovery of the metal ion with the highest log K.

The findings in this study contribute to the understanding of the fundamental characteristics of chelating surfactants, which can be further utilized in practical applications.

Place, publisher, year, edition, pages
sundsvall: Mid Sweden University, 2014. 48 p.
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 179
Keyword
chelating surfactant, DTPA based surfactant, pH-responsive, characterization, surface tension, NMR diffusometry, conditional stability constants, interaction parameter, ion flotation
National Category
Physical Chemistry
Identifiers
urn:nbn:se:miun:diva-21405 (URN)978-91-87557-39-2 (ISBN)
Public defence
2014-03-21, Sal M102, Mittuniversitetet, sundsvall, 10:15 (English)
Opponent
Supervisors
Available from: 2014-02-20 Created: 2014-02-20 Last updated: 2014-02-20Bibliographically approved

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