Antonov Alexander P, Musacchio Marco, Löwen Hartmut, Caprini Lorenzo
Institut für Theoretische Physik II: Weiche Materie, Heinrich-Heine-Universität Düsseldorf, Universitätsstraße 1, D-40225, Düsseldorf, Germany.
Physics department, University of Rome La Sapienza, P.le Aldo Moro 5, IT-00185, Rome, Italy.
Nat Commun. 2025 Aug 6;16(1):7235. doi: 10.1038/s41467-025-62626-9.
Cooling processes in nature are typically generated by external contact with a cold reservoir or bath. According to the laws of thermodynamics, the final temperature of a system is determined by the temperature of the environment. Here, we report a spontaneous internal cooling phenomenon for active particles, occurring without external contact. This effect, termed self-sustained frictional cooling, arises from the interplay between activity and dry (Coulomb) friction, and in addition is self-sustained from particles densely caged by their neighbors. If an active particle moves in its cage, dry friction will stop any further motion after a collision with a neighbor particle thus cooling the particle down to an extremely low temperature. We demonstrate and verify this self-sustained cooling through experiments and simulations on active granular robots and identify dense frictional arrested clusters coexisting with hot, dilute regions. Our findings offer potential applications in two-dimensional swarm robotics, where activity and dry friction can serve as externally tunable mechanisms to regulate the swarm's dynamical and structural properties.
自然界中的冷却过程通常是通过与冷源或冷浴的外部接触产生的。根据热力学定律，系统的最终温度由环境温度决定。在此，我们报告了活性粒子的一种自发内部冷却现象，该现象在无外部接触的情况下发生。这种效应，称为自持摩擦冷却，源于活性与干（库仑）摩擦之间的相互作用，此外还由被其邻居紧密束缚的粒子自持。如果一个活性粒子在其笼子中移动，干摩擦会在与相邻粒子碰撞后阻止其进一步运动，从而将粒子冷却到极低温度。我们通过对活性颗粒机器人的实验和模拟来演示和验证这种自持冷却，并识别出与热的、稀疏区域共存的密集摩擦停滞簇。我们的发现为二维群体机器人技术提供了潜在应用，其中活性和干摩擦可作为外部可调机制来调节群体的动力学和结构特性。
