Smectic Liquid Crystalline Phase Behavior of Silica Nanorods Dispersed in DMSO and Water

T. Xu, V.A. Davis
Auburn Unviersity, US

Keywords: smectic, liquid crystal, nanorod, silica, rheology

Summary:

Silica nanoparticles have excellent thermal, electronic, optical, optoelectronic properties. However, manufacturing them into dielectric films or optoelectronic devices requires better understanding of the phase behavior and shear response of silica nanorod dispersions. We report smectic liquid crystalline phase formation in dispersions of low aspect ratio nanorods dispersed in binary mixtures of dimethyl sulfoxide (DMSO) and water (H2O). The experimental phase diagram shows the phase behavior is highly affected by the DMSO concentration. Below a critical DMSO concentration, the system is initially biphasic, but forms crystal solvates at higher concentrations. At higher DMSO concentration, dispersion rheology is consistent with the key rheological characterizations for rodlike polymer lyotropic liquid crystals. The addition of ~ 9 vol. % silica to 90/10 DMSO/H2O resulted in a biphasic system with a low shear viscosity over three orders of magnitude greater than that of the solvent. Different dispersion microstructures were observed, depending on whether the nanorod polydispersity was reduced through sedimentation. The microstructure of coatings prepared from the dispersions were dependent on the concentration and shear. These studies on the phase behavior and processing methods provide a foundation for establishing manufacturing routes for large area nanorod coatings with controlled microstructures and properties.