Oral: Understanding and Controlling the Collective Behaviors of Quincke Rollers via Humidity and Temperature

Active materials often exhibit collective behaviors that emerge at the group level, which are not present in individual units. While extensive studies have been conducted on collective behaviors under ideal conditions, the complexities of real-world environments cannot be overlooked. In this study, we investigate the Quincke rollers system to clarify how external environmental factors, such as temperature and humidity, influence the electrodynamic processes of the system, leading to diverse self-organizing collective behaviors such as vortex, turbulence, polar clusters and active crystal. In particular, temperature and humidity of the environment alter the system's electrical properties such as the electrical conductivity and dielectric permittivity of the organic medium, thereby affecting the four types of pairwise interactions: dipolar repulsion, dielectrophoresis, electrohydrodynamic attraction and hydrodynamic interactions. As a result, increasing the environmental humidity or temperature, shifts the collective behaviors from vortex to polar cluster and finally to active crystal. Additionally, we demonstrate in-situ control of these collective behaviors by leveraging the system's sensitivity to environmental changes. This research offers new insights into the interactions between active materials and complex environments and paves the way for practical applications of Quincke roller systems.