Observations of orientational ordering in aqueous suspensions
of a nano-layered silicate
Fossum JO, Gudding E, Fonseca DDM, Meheust Y, DiMasi E,
Gog T, Venkataraman C
ENERGY |
30 (6): 873-883 MAY 2005 |
|
Abstract:
We have studied colloidal suspensions of clay particles in aqueous salt solutions.
These Suspensions make excellent model systems for the study of interactions
between plate-shaped particles, due to the inherent possibility of tuning
their electrostatic repulsion with the concentration of the salt. Various
gel and sol structures are possible, including nematic liquid crystalline
order, although only qualitative identification of the latter in clay colloids
has been available so far. Here, we briefly review our earlier synchrotron
X-ray diffraction from gravity dispersed solutions of Na fluorohectorite,
a synthetic swelling clay, over a large NaCl concentration range. Our use
of liquid X-ray scattering techniques allowed us to identify regions in which
particles reorient from horizontal to vertical alignments in strata coexisting
at different heights within the sample. We thus identified two distinct gel
regions characterized by differences in orientational anisotropy and domain
size. In addition, we for the first time, present visual observations of
birefringence in these systems; these new observations support the interpretation
of our X-ray experiments, and thus our new results provide further evidence
for nematic order. (C) 2004 Elsevier Ltd. All rights reserved.
