Mechanical Properties of Hydrogel Beads

Disordered dense packing of bubbles, droplets and grains form fragile solids that can withstand small stresses by virtue of system-wide force~chains that lock the system into a jammed state. The nature of force chains in soft materials has been the subject of intense research, but despite much effort, a deep understanding of the jamming transition remains elusive. In this experiment we study the mechanical properties of hydrogel beads to explore these particles as force~chain transducers in densely packed systems. The experiment consists of uniaxial compression of hydrogel beads under a known force, measuring the strain and the radius of the contact area of the bead. A linear relationship exists between the contact radius and the strain, and two separate regimes determine the relationship between the force and the strain. Using the relationships found, a universal power law is being determined to describe the force as a function of the contact radius of the beads.