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Anomalies in Solution Behavior of an Alkyl Aminopolycarboxylic Chelating Surfactant
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.
2013 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 45, 13708-13716 p.Article in journal (Refereed) Published
Abstract [en]

The solution behavior of a DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant, 4-C12-DTPA, has beenstudied by tensiometry and NMR diffusometry. In the absence of metalions, the eight donor atoms in the headgroup are titrating, and thecharge of the headgroup can thus be tuned by altering the pH. 4-C12-DTPA changes from cationic at very low pH, over a number ofzwitterionic species as the pH is increased, and eventually becomesanionic at high pH. Around the isoelectric point, the chelatingsurfactant precipitated. The solution properties, studied above thesolubility gap, were found strongly pH dependent. When increasing theamount of negative charges in the headgroup, by increasing the pH, theadsorption efficiency was reduced and the cmc was increased. Anoptimum in surface tension reduction was found at pH 5, due to aproper balance between protonated and dissociated groups. Anomaliesbetween surface tension measurements and NMR diffusometry in determination of cmc revealed a more complex relationbetween surface tension, surface coverage, and cmc than usually considered, which is not in line with the common interpretationof the Gibbs adsorption equation. At some of the investigated pH levels, measurements of bulk pH could confirm the location ofcmc, due to the increased protonation of micelles compared to monomers in solution. The adsorption of monomers to the air−water interface showed unusually slow time dependence, evident from decreasing surface tension for several hours. This isexplained by rearrangements of the large head groups to reduce the headgroup area and increase the packing parameter.

Place, publisher, year, edition, pages
2013. Vol. 29, no 45, 13708-13716 p.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:miun:diva-20289DOI: 10.1021/la4024508ISI: 000327044600007Scopus ID: 2-s2.0-84887573543OAI: oai:DiVA.org:miun-20289DiVA: diva2:666371
Available from: 2013-11-22 Created: 2013-11-22 Last updated: 2014-04-23Bibliographically 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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