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Predicting the Critical Micelle Concentrations of Aqueous Solutions of Ionic Liquids and Other Ionic Surfactants

  1. U. Preiss1,
  2. C. Jungnickel Dr.2,
  3. J. Thöming Prof. Dr.3,
  4. Ingo Krossing Prof. Dr.1,
  5. J. Łuczak2,
  6. M. Diedenhofen Dr.4,
  7. A. Klamt Dr.4,5

Article first published online: 23 JUL 2009

DOI: 10.1002/chem.200900024

Issue

Chemistry - A European Journal

Chemistry - A European Journal

Volume 15, Issue 35, pages 8880–8885, September 7, 2009

Additional Information

How to Cite

Preiss, U., Jungnickel, C., Thöming, J., Krossing, I., Łuczak, J., Diedenhofen, M. and Klamt, A. (2009), Predicting the Critical Micelle Concentrations of Aqueous Solutions of Ionic Liquids and Other Ionic Surfactants. Chemistry - A European Journal, 15: 8880–8885. doi: 10.1002/chem.200900024

Author Information

  1. 1

    Institute of Inorganic and Analytical Chemistry, University of Freiburg, Albertstrasse 21, 79104 Freiburg (Germany), Tel.: (+49) 761-2036121

  2. 2

    Chemical Faculty, Gdańsk University of Technology ul. G. Narutowicza 11/12, 80-233 Gdańsk (Poland)

  3. 3

    UFT—Centre for Environmental Research and Technology, University of Bremen, Leobener Strasse, 28359 Bremen (Germany)

  4. 4

    COSMOlogic GmbH & Co. KG, Burscheider Strasse 515, 51381 Leverkusen (Germany)

  5. 5

    Institute of Physical and Theoretical Chemistry, University of Regensburg, Universitätsstrasse 31, 93040 Regensburg (Germany)

Publication History

  1. Issue published online: 1 SEP 2009
  2. Article first published online: 23 JUL 2009
  3. Manuscript Revised: 20 MAY 2009
  4. Manuscript Received: 5 JAN 2009

Funded by

  • Albert-Ludwigs-Universität Freiburg
  • DFG priority program. Grant Number: SPP 1191
  • Polish Ministry of Education and Research. Grant Number: N205 041 32/2340

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Keywords:

  • density functional calculations;
  • ionic liquids;
  • micelles;
  • molecular volume;
  • surfactants

Graphical Abstract

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Predicting CMCs! A new method for predicting the critical micelle concentrations of ionic liquids and other ionic surfactants that is free from any need for experimental input is presented, extending common volume-based thermodynamics equations to include different interaction enthalpies calculated by COSMO-RS.

Abstract

Some ionic liquids (ILs) are structurally analogous to surfactants, especially those that consist of a combination of organic and inorganic ions. The critical micelle concentration (CMC) is a basic parameter of surface chemistry and colloid science. A significant amount of research has already been carried out to determine the CMCs of ILs. However, because of the many varied cation/anion combinations, it is a daunting task to measure the CMCs of all possible ILs. Herein we suggest a general rule for predicting the CMCs of ionic surfactants in water based on data from COSMO-RS calculations. In accordance with the Stauff–Klevens rule, the molecular volume (Vm) is sufficient to describe similar homologous series of cationic surfactants such as imidazolium- and ammonium-based ionic liquids with varying side-chain lengths. However, to also include anionic surfactants like Na[CnSO4] in a more general correlation, Vm has to be exchanged by the cubed molecular radius (equation image) and the molecular surface has to be used as an additional descriptor. Furthermore, to describe double amphiphilic compounds like [C4MIm][C8SO4], the enthalpies of mixtures calculated by COSMO-RS have to be taken into account. The resulting equation had allowed us to predict the CMCs of all of the 36 tested surfactants with an error similar to or smaller than the usual experimental errors (18 different cations, 10 different anions: root mean squared error (rmse)=0.191 logarithmic units; R2=0.994). We discuss the factors governing micelle formation on the basis of our calculations and show that the structure of our equation can be related to Gibbs’ theory of crystallization.

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