Flocking results from dynamical alignment among neighbors in a collection of active self-propelling objects. The intervening medium, typically a fluid, however, is not considered to be important for alignment, except for acting as a momentum sink. The flocking system is therefore described as momentum nonconserving"dry"active matter. Here we investigate a confined system of self-propelled Marangoni swimmers where feedback from the fluid medium, which crucially depends on the shape of the swimmers, influences their alignment. Using up to thirty partially camphor-coated triangular paper boats as polar swimmers, we uncover a disorder-to-order transition, and an unusual re-entrant order-to-disorder transition, as functions of camphor concentration and swimmer density, respectively. We reproduce these transitions by formulating a reaction-diffusion model for the camphor field, coupled to the swimmer dynamics, where propulsion forces arise from surface tension gradients. The shape-dependent hydrodynamic interaction discussed here could be central to efficient flocking in living organisms too.
Active matter, i.e., nonequilibrium systems that transform non-thermal energy from the environment into self-propulsion or other functional mechanisms, has attracted the attention of the statistical physics community in recent decades. Flocking, as shown by the aerial displays of starling flocks, is perhaps one of the...
Abstract Content of image described in text. Transport phenomena in swimmer suspensions are ubiquitous in biological environments. In this study, we numerically investigate the transport of swimmers modelled as squirmers in semi-dilute suspensions, with a particular focus on the effects of fluid inertia and sedimentati...
Yan Xia, Zhao-Wu Lin, Zhao-Sheng Yu et al.· Journal of Fluid Mechanics· 0 citations
We develop a continuum theory for a fluid of elongated particles that advance along their own axes. The same kinematics is ideally shared by flocks of sheep, self-propelled rods, vehicular traffic, and turning flocks of birds. Within the framework of continua with vectorial microstructure, in which each point also carr...
Abstract Content of image described in text. Swimming microorganisms dynamically respond to their external environment, resulting in self-organised collective behaviour. To accurately predict the flow field at the continuum scale, it is essential to understand the rheological properties of active suspensions. Microorga...
Kiyoto Kubo, Toshihiro Omori, T. Ishikawa· Journal of Fluid Mechanics· 0 citations
Active flows are often confined by soft, deformable boundaries that they can push against, reshape, and in turn get reorganized by. Motivated by this interplay, we combine theory and numerical simulations to analyze the morphodynamics of an elastic vesicle enclosing a dilute suspension of extensile active particles. We...
A flock of chemical micromotors is potentially useful for drug delivery and environmental sensing, but realizing this potential is often hindered by uncontrolled clustering due to phoresis/osmosis. Here, we decouple the propulsion and head-to-head repulsion in chemically powered micromotors, enabling highly ordered flo...
Zhi-Ying Yi, De-Zhou Cao, Xing Ma et al.· Small· 0 citations
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