Liquid crystalline aqueous suspensions of V2O5 ribbons: From repulsive sols to attractive gels

Abstract

Colloidal aqueous suspensions of vanadium pentoxide (V2O5) ribbons form a liquid crystalline nematic phase at volume fractions φ > 0.5%. We investigate the influence of increasing ionic strength on the colloidal stability of these suspensions. Salt addition brings about the flocculation of these suspensions in agreement with DLVO theory. Moreover, salt addition below the flocculation threshold leads to gelation and so fluid sols can be turned into gels upon increasing ionic strength. This gelation can be understood as the first sign of attractive forces which become increasingly important as electrostatic repulsions are screened. However, ion-specific effects were also observed which suggests that a general model of these phenomena is still out of reach. © Springer-Verlag 1999.