Abstract
Autonomous motion and motility are hallmarks of active matter. Active agents, such as biological cells and synthetic colloidal particles, consume internal energy or extract energy from the environment to generate self-propulsion and locomotion. These systems are persistently out of equilibrium due to continuous energy consumption. It is known that pressure is not always a state function for generic active matter. Torque interaction between active constituents and confinement renders the pressure of the system a boundary-dependent property. The mechanical pressure of anisotropic active particles depends on their microscopic interactions with a solid wall. Using self-propelled dumbbells confined by solid walls as a model system, we perform numerical simulations to explore how variations in the wall stiffness influence the mechanical pressure of dry active matter. In contrast to previous findings, we find that mechanical pressure can be independent of the interaction of anisotropic active particles with walls, even in the presence of intrinsic torque interaction. Particularly, the dependency of pressure on the wall stiffness vanishes when the stiffness is above a critical level. In such a limit, the dynamics of dumbbells near the walls are randomized due to the large torque experienced by the dumbbells, leading to the recovery of pressure as a state variable of density.
Highlights
IntroductionAs mechanical pressure results from the collision of particles with a wall, a fundamental understanding of how wall stiffness affects the near-wall dynamics of active particles and modulates the transferred linear momentum is critical for elucidating the origin of active pressure[34,35,36]
We applied numerical simulation to investigate the influences of wall stiffness on the mechanical pressure generated by anisotropic self-propelled particles with intrinsic torque interaction
Our results show that the mechanical pressure near the wall decreases with increasing wall stiffness, and more importantly, reaches a constant plateau above a certain stiffness
Summary
As mechanical pressure results from the collision of particles with a wall, a fundamental understanding of how wall stiffness affects the near-wall dynamics of active particles and modulates the transferred linear momentum is critical for elucidating the origin of active pressure[34,35,36]. This work explores the impact of stiffness variation on the mechanical pressure of a dry, underdamped system of self-propelled dumbbells, which possess intrinsic torque interaction with walls. Through a systematic variation of the particle number density and the wall stiffness, we demonstrate that pressure follows the prediction of an EOS at high stiffnesses, even for anisotropic particles. The microscopic origin of the recovery of the EOS is further explored based on single collision events, which reveal the profound effect of single particle dynamics on the momentum transfer and the particle density near the wall. Our results shed light onto the unusual features of active pressure and pave the way for manipulating the pressure of active systems in various engineering applications
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