The motion of a particle through a collection of hydrogels: from a liquid to a solid.

We report the results of an experimental investigation of the motion of a solid particle through a collection of hydrogel particles in water. The volume of fluid is kept fixed in each run of the experiment and the number of particles is changed to set the volume fraction. Fluid-like behaviour is found at small volume fractions and visco-elastic properties are found at higher particle concentrations. Slowing of the motion, including divergence in the propagation speed is found at intermediate volume fractions. This is accompanied by an intriguing linear speed dependence over a small range of volume fractions.