Hydrodynamic Spin-Pairing and Active Polymerization of Oppositely Spinning Rotors

TL;DR

This study investigates how mixed populations of oppositely spinning rotors self-organize into active chains called gyromers, revealing new insights into their collective dynamics driven by fluid motion and steric interactions.

Contribution

It introduces the concept of gyromers formed by oppositely spinning rotors and provides experimental, numerical, and analytical evidence of their self-assembly and dynamics.

Findings

Oppositely spinning rotors form stable active chains called gyromers.

Same-spin rotors repel and orbit each other, while opposite spins form bound pairs.

The minimal model predicts gyromer formation and potential secondary structures.

Abstract

Rotors are common in nature - from rotating membrane-proteins to superfluid-vortices. Yet, little is known about the collective dynamics of heterogeneous populations of rotors. Here, we show experimentally, numerically, and analytically that at small but finite inertia, a mixed population of oppositely spinning rotors spontaneously self-assembles into active chains, which we term gyromers. The gyromers are formed and stabilized by fluid motion and steric interactions alone. A detailed analysis of pair interaction shows that rotors with the same spin repel and orbit each other while opposite rotors spin-pair and propagate together as bound dimers. Rotor dimers interact with individual rotors, each other, and the boundaries to form chains. A minimal model predicts the formation of gyromers in numerical simulations and their possible subsequent folding into secondary structures of lattices and rings. This inherently out-of-equilibrium polymerization process holds promise for engineering self-assembled metamaterials such as artificial proteins.