DOI: 10.1051/jp2:1995200
J. Phys. II France 5 (1995) 1577-1596

A Structural Study of the Lyotropic Nematic Phase of Vanadium Pentoxide Gels

P. Davidson^{1, 2}, C. Bourgaux³, L. Schoutteten¹, P. Sergot⁴, C. Williams³ and J. Livage<sup>5

1</sup>  Laboratoire de Physique des Solides URA 002, Bat. 510, Université Paris Sud, 91405 Orsay Cedex, France
²  Materials Department, University of California, Santa Barbara, CA 93106, USA
³  Laboratoire pour l'Utilisation du Rayonnement Electromagnétique UMR 130, Bat. 209D, Université Paris-Sud, 91405 Orsay Cedex, France
⁴  Laboratoire de Physicochimie des Macromolécules URA 278, Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris, 10 rue Vauquelin, 75231 Paris Cedex 05, France
⁵  Laboratoire de Chimie de la Matière Condensée URA 1466, Université Pierre et Marie Curie, 4 Place Jussieu, 75252 Paris, France

(Received 20 April 1995, accepted 30 May 1995)

Abstract
The aqueous suspensions of vanadium pentoxide ribbons are known to present a lyotropic nematic phase. The optical microscopy photographs of these suspensions in the gel and the sol states shown in this paper are indeed typical nematic textures. The biphasic (I/N) region shows tactoids which can be aligned by a magnetic field. Small angle X-ray scattering (SAXS) experiments were performed either on unoriented samples or on samples aligned by shear flow. The scattering is comparable to that of the other classic lyotropic nematic phases displayed by stiff organic rod-like particles. Scattering patterns give information on the transverse dimensions of the ribbons and on the average distance between them as a function of concentration. Estimates of the nematic order parameter were also obtained. Finally, the relevance of Onsager's model is discussed; the importance of the electrostatic interactions between ribbons in the onset of the nematic ordering of this system is stressed.

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