Volume 48, Number 1, October I 1999
|Page(s)||53 - 59|
|Section||Condensed matter: structure, mechanical and thermal properties|
|Published online||01 September 2002|
The effect of attractive interactions on the nematic order of gels
Laboratoire de Physique des Solides, Bât. 510, URA 002 CNRS, Université Paris Sud 91405 Orsay cedex, France
2 Laboratoire pour l'Utilisation du Rayonnement Electromagnétique, Bât. 209D UMR 130 CNRS, Université Paris Sud - 91405 Orsay cedex, France
3 Laboratoire de Chimie de la Matière Condensée, URA 1466 CNRS Université Pierre et Marie Curie - 4 Place Jussieu, 75252 Paris cedex, France
Accepted: 26 July 1999
Aqueous suspensions of ribbons form a lyotropic nematic phase at volume fractions larger than 0.7%. We investigate the effect of adding a monovalent salt (NaCl) to this charge-stabilized system. Without any added salt, the nematic ordering can be described by the Onsager model based on a hard-core repulsive potential. Adding salt induces the gelation of these suspensions. Very unexpectedly, it also induces the stabilization of the nematic phase with respect to the isotropic one in a way opposite to the predictions of the Onsager model and to the usual behavior of typical hard-rod fluids. Larger salt concentrations eventually lead to flocculation. These observations indicate the increasing influence of attractive interactions which we argue are most probably van der Waals attractions.
PACS: 61.30.-v – Liquid crystals / 82.70.Dd – Colloids / 82.70.Gg – Gels and sols
© EDP Sciences, 1999
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