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

Abstract

\nThe 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.\n