Distortion and destruction of colloidal flocks in disordered environments

By A. Morin, N. Desreumaux, Jean-Baptiste Caussin, Denis Bartolo. Nature Physics, 2016

172 citations recorded by the source corpus.

Our understanding of collective animal behaviour generally assumes that flocks and herds move through homogeneous environments. Colloidal experiments suggest that flocking can be distorted or even suppressed by the introduction of disorder. How do flocks, herds and swarms move through disordered environments? The answer to this question is crucial not only to animal groups in the wild, but also to effectively all applications of collective robotics and active materials composed of synthetic motile units1,2,3,4,5,6,7,8,9,10,11,12,13,14. In stark contrast, aside from rare exceptions15,16,17, our physical understanding of flocking has so far been limited to homogeneous media18,19,20. Here we explain how collective motion survives in geometrical disorder. To do so, we combine experiments and analytical theory to examine motile colloids cruising between randomly positioned microfabricated obstacles. We elucidate how disorder and bending elasticity compete to channel the flow of polar flocks along sparse river networks akin those found beyond plastic depinning in driven condensed matter21. Further increasing the disorder, we demonstrate that collective motion is suppressed in the form of a first-order phase transition generic to all polar active materials.

Subfields: Condensed Matter Physics, Materials Chemistry, Mechanical Engineering

View Paper: https://www.semanticscholar.org/paper/b8be438bd2038ee4593d82df8f74909eb6753dcc