System size dependence in hydrogel sphere packing relaxation behaviour during cyclic loading*

Cyclic loading of amorphous particle packings induces many nontrivial mechanical effects including memory and hysteresis. Here we aim to study the emergence of such effects by experimentally probing the role of system size on the collective mechanics of soft particle packings. Hydrogel sphere packings are packings of soft, slippery spheres and therefore a model system that is one of the closest experimental realizations of an idealized granular packing. Despite their ideal behavior, hydrogel sphere packings already reveal system size dependence in their relaxation behavior. We find that individual hydrogel particles display very different relaxation behavior than packings of even four hydrogel spheres. We discuss how such collective effects get amplified with packing size and are influenced by other experimental settings such as the particle properties.