Europhys. Lett, 48 (1), pp. 53-59 (1999)
The effect of attractive interactions on the nematic order of gels
O. Pelletier 1, P. Davidson 1, C. Bourgaux 2 and J. Livage 3
1 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
(received 3 May 1999; accepted in final form 26 July 1999)
PACS. 61.30 - Liquid crystals.
PACS. 82.70Dd - Colloids.
PACS. 82.70Gg - Gels and sols.
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.
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