Dynamics and rheology at micro and macro scales of colloidal rod gels

Colloidal rod suspensions form gels or other arrested states at relatively low volume fractions, making them excellent rheological modifiers and useful as models to understand complex systems like networks of biopolymer filaments. We use both macro- and micro-rheology methods to characterize colloidal rods made of polyamide. We use the microrheology technique, differential dynamic microscopy (DDM), which combines elements of video microscopy and dynamic light scattering. We compare our DDM microrheology with macroscopic bulk rheology to make connections between microscale dynamics and bulk mechanical properties, connections which have been built for colloidal gels of spherical particles, but which are more challenging to make with anisotropic particles. We directly compare quantities from microrheology analysis such as non-ergodicity parameters, confinement lengths, timescales of the floppiest mode, and degrees to which diffusion is anomalous to macro-rheological properties like the viscoelastic moduli. We present data across multiple rod aspect ratios, from approximately 20 to 300, and concentrations with suspensions exhibiting dynamics from purely diffusive to subdiffusive to non-ergodic.