Microscale Yielding in Colloidal Rod Gels of Bacterial Cellulose Nanofibers

High aspect ratio colloids can form elastic structures at amazingly low volume fractions, and there is an expectation that rod systems could be much more efficient than gels made from spherical colloids. However, the lowest measured gel volume fractions for rods and spheres tend to be of similar magnitude. We examine the theoretical expectation of percolation structures for rods and spheres and compare against active microrheological measurements of a bacterial cellulose network in water.  The mechanism and rate of yielding by the fiber network is shown to vary in a way consistent with a two-fluid model and our measurements are used to build on previous observations of higher suspension efficiency for sparse gels than for dense colloidal glasses.