(421c) Thermoreversible Gels of Hollow Silica Nanorod Dispersions

Colloidal suspensions composed of anisotropic particles are widely utilized in consumer products, coatings, cements, food products, and pharmaceuticals. Consequently, there is a need to quantitatively understand the effects of particle shape on the gel and glass transitions, particularly for suspensions of anisotropic colloids with lower aspect ratios (L/D ~ 1-10). Prior studies identified gravitational settling as an issue in identifying the gel transition, especially for low-volume fractions. Here, we present a new thermoreversible colloidal system composed of hollow, octadecyl-coated silica rods of 30nm diameter with controlled aspect ratio and thermoreversible short-range attractions. Rheology and dynamic light scattering measurements on suspensions of these model, hollow adhesive hard rods (AHR) of aspect ratio ~3 suspended in tetradecane exhibit thermoreversible gelation without the complicating effects of gravitational settling. Small angle neutron scattering measurements of the microstructure are analyzed to determine the strength of attraction in the form of a Baxter sticky parameter. Lastly, the results on the hollow AHR system are mapped into a dimensionless state diagram to compare with previous predictions of attraction-driven gels, repulsion-driven glasses, and liquid crystal phases and provide guidance for the effects of aspect ratio on gelation.