Advanced

Tactoid Formation in Montmorillonite

Segad, Mo LU ; Jönsson, Bo LU and Cabane, B. (2012) In Journal of Physical Chemistry C 116(48). p.25425-25433
Abstract
Aqueous dispersions of Ca montmorillonite contain small clusters of clay platelets, often named "tactoids". In these tactoids, the platelets are arranged parallel to each other with a constant spacing of 1 nm. We have used small-angle X-ray scattering (SAXS) to determine the average number of platelets per tactoid, < N >. We found that this number depends on the platelet size, with larger platelets yielding larger tactoids. For a dispersion in equilibrium with a mixed electrolyte solution, the tactoid size also depends on the ratio of divalent to monovalent cations in the reservoir. Divalent counterions are strongly favored in this competition and will accumulate in the tactoids. In dispersions of pure sodium montmorillonite, that... (More)
Aqueous dispersions of Ca montmorillonite contain small clusters of clay platelets, often named "tactoids". In these tactoids, the platelets are arranged parallel to each other with a constant spacing of 1 nm. We have used small-angle X-ray scattering (SAXS) to determine the average number of platelets per tactoid, < N >. We found that this number depends on the platelet size, with larger platelets yielding larger tactoids. For a dispersion in equilibrium with a mixed electrolyte solution, the tactoid size also depends on the ratio of divalent to monovalent cations in the reservoir. Divalent counterions are strongly favored in this competition and will accumulate in the tactoids. In dispersions of pure sodium montmorillonite, that are equilibrated with a mixture of Na+ and Ca2+ cations, the Na+ cations initially cause a repulsion between the platelets, but the divalent ions rapidly replace the monovalent ones and lead to the formation of tactoids, typically within less than one hour based on the divalent to monovalent ratio. This cation exchange as well as tactoid formation can be semiquantitatively predicted from Monte Carlo simulations. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Journal of Physical Chemistry C
volume
116
issue
48
pages
25425 - 25433
publisher
The American Chemical Society
external identifiers
  • wos:000311921900032
  • scopus:84870776513
ISSN
1932-7447
DOI
10.1021/jp3094929
language
English
LU publication?
yes
id
cd3142c7-e8c6-4714-a511-5e1407c5cc57 (old id 3371989)
date added to LUP
2013-02-01 10:45:39
date last changed
2017-08-06 03:06:05
@article{cd3142c7-e8c6-4714-a511-5e1407c5cc57,
  abstract     = {Aqueous dispersions of Ca montmorillonite contain small clusters of clay platelets, often named "tactoids". In these tactoids, the platelets are arranged parallel to each other with a constant spacing of 1 nm. We have used small-angle X-ray scattering (SAXS) to determine the average number of platelets per tactoid, &lt; N &gt;. We found that this number depends on the platelet size, with larger platelets yielding larger tactoids. For a dispersion in equilibrium with a mixed electrolyte solution, the tactoid size also depends on the ratio of divalent to monovalent cations in the reservoir. Divalent counterions are strongly favored in this competition and will accumulate in the tactoids. In dispersions of pure sodium montmorillonite, that are equilibrated with a mixture of Na+ and Ca2+ cations, the Na+ cations initially cause a repulsion between the platelets, but the divalent ions rapidly replace the monovalent ones and lead to the formation of tactoids, typically within less than one hour based on the divalent to monovalent ratio. This cation exchange as well as tactoid formation can be semiquantitatively predicted from Monte Carlo simulations.},
  author       = {Segad, Mo and Jönsson, Bo and Cabane, B.},
  issn         = {1932-7447},
  language     = {eng},
  number       = {48},
  pages        = {25425--25433},
  publisher    = {The American Chemical Society},
  series       = {Journal of Physical Chemistry C},
  title        = {Tactoid Formation in Montmorillonite},
  url          = {http://dx.doi.org/10.1021/jp3094929},
  volume       = {116},
  year         = {2012},
}