Rheology and Shear-Induced Textures of Silver Nanowire Lyotropic Liquid Crystals

Abstract

We report the rheological and microstructural shear response of a mixture of polyvinylpyrrolidone (PVP) coated silver nanowires and nanoparticle aggregates (Ag) dispersed in ethylene glycol (EG) or water (H2O). Biphasic and liquid crystalline dispersions exhibited rheological characteristics similar to those of lyotropic liquid crystalline polymers (LCPs). The viscosity versus concentration curve for Ag-EG dispersions showed a viscosity minimum at a silver concentration between 2.2 vol.% and 2.9 vol.%; this is indicative of the transition to an entirely liquid crystalline phase. The rheology results were consistent with optical microscopy observations that at 2.9 vol.% the sample was entirely birefringent; this is another indication of liquid crystalline phase formation. Shear had a significant effect on the microstructure of the dispersions and dried coatings. Depending on the shear rate, worm or shear banding Structures were observed.