Far-Field Flow Forces Attraction

Abstract

L ong-range attraction between distant objects can arise from gravitational or electrostatic forces. For objects suspended in active fluids—those containing a large number of tiny motile particles—efforts to understand how these forces drive effective interactions focus on direct collisions between the objects and the active agents. Now Luhui Ning and Yi Peng of the Chinese Academy of Sciences and their colleagues show that indirect effects can also play an important role in generating long-range attraction [1]. By examining the effective interactions between two plates immersed in a bacterial suspension, they show that hydrodynamic forces generated by swimming bacteria have a strong influence on the plates’ behaviors. The results open a new pathway toward developing active fluids to manipulate interactions between passive objects, a common objective in biomedicine andmaterials science.