Activity Jamming

Active systems, which harness energy from their environment, offer a promising pathway for designing functional materials with tunable bulk properties through engineered microscopic interactions. To date, however, most active systems have been constrained by either their manufacturing scalability or their ability to generate and sustain sufficiently large stresses to influence bulk behavior, making the investigation of 3D bulk properties challenging. In this study, we overcome these constraints by engineering three-dimensional active solids composed of a suspension of micron-scale Quincke rotors. Our experiments reveal that at sufficiently intermediate volume fractions Quincke rotors undergo motility-induced phase separation into dense and dilute regions. This motility induced phase separation is sufficient to jam the suspension even when the suspension volume fraction is well below the threshold required for shear induced jamming. Finally, we present a phase diagram for activity jamming as a function of volume fraction and applied stress. Our findings could provide new insights into jamming mechanisms that may be at play in other active systems in physics and biology.