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Titration of fatty acids solubilized in cationic and anionic micelles. Calorimetry and thermodynamic modeling

Söderman, Olle LU ; Jönsson, Bengt LU and Olofsson, Gerd LU (2006) In The Journal of Physical Chemistry Part B 110(7). p.3288-3293
Abstract
The electrostatic properties of charged surfactant micelles are investigated through titrations of fatty acid probes solubilized in the micelles. The titration process is followed by means of calorimetric measurements and by determining the pH values as a function of added base. This approach yields a complete thermodynamic description of the titration process. In particular, we find that the process is endothermic at 298 K. This is contrary to the titration of carboxylic acids in water, where Delta H is approximately 0. To identify the main effect underlying the difference in Delta H between titration in a micelle and water, a thermodynamic model has been developed which focuses on the transfer properties of charged and uncharged species... (More)
The electrostatic properties of charged surfactant micelles are investigated through titrations of fatty acid probes solubilized in the micelles. The titration process is followed by means of calorimetric measurements and by determining the pH values as a function of added base. This approach yields a complete thermodynamic description of the titration process. In particular, we find that the process is endothermic at 298 K. This is contrary to the titration of carboxylic acids in water, where Delta H is approximately 0. To identify the main effect underlying the difference in Delta H between titration in a micelle and water, a thermodynamic model has been developed which focuses on the transfer properties of charged and uncharged species from bulk water to the surface of a micelle and which incorporates a dielectric discontinuity at the micellar surface. The model relies on the use of the Poisson-Boltzmann equation which is solved using a finite element method. Experimental results and the model calculations imply that the dielectric discontinuity at (or near) the micellar surface plays a major role and hence must be included when analyzing the titration behavior of an acid functionality at the surface of a charged micelle. (Less)
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publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
110
issue
7
pages
3288 - 3293
publisher
The American Chemical Society (ACS)
external identifiers
  • wos:000235560900050
  • scopus:33644921493
ISSN
1520-5207
DOI
10.1021/jp056861h
language
English
LU publication?
yes
id
ccbf5d2e-44ae-49f8-94d0-18eb4f9eea72 (old id 417091)
date added to LUP
2016-04-01 16:51:27
date last changed
2021-02-17 07:38:28
@article{ccbf5d2e-44ae-49f8-94d0-18eb4f9eea72,
  abstract     = {The electrostatic properties of charged surfactant micelles are investigated through titrations of fatty acid probes solubilized in the micelles. The titration process is followed by means of calorimetric measurements and by determining the pH values as a function of added base. This approach yields a complete thermodynamic description of the titration process. In particular, we find that the process is endothermic at 298 K. This is contrary to the titration of carboxylic acids in water, where Delta H is approximately 0. To identify the main effect underlying the difference in Delta H between titration in a micelle and water, a thermodynamic model has been developed which focuses on the transfer properties of charged and uncharged species from bulk water to the surface of a micelle and which incorporates a dielectric discontinuity at the micellar surface. The model relies on the use of the Poisson-Boltzmann equation which is solved using a finite element method. Experimental results and the model calculations imply that the dielectric discontinuity at (or near) the micellar surface plays a major role and hence must be included when analyzing the titration behavior of an acid functionality at the surface of a charged micelle.},
  author       = {Söderman, Olle and Jönsson, Bengt and Olofsson, Gerd},
  issn         = {1520-5207},
  language     = {eng},
  number       = {7},
  pages        = {3288--3293},
  publisher    = {The American Chemical Society (ACS)},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Titration of fatty acids solubilized in cationic and anionic micelles. Calorimetry and thermodynamic modeling},
  url          = {http://dx.doi.org/10.1021/jp056861h},
  doi          = {10.1021/jp056861h},
  volume       = {110},
  year         = {2006},
}