Abstract
We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field. Both the speed and direction of the self-propulsion, and the strength of the attractive interaction between particles can be controlled by tuning the frequency of the applied electric field and the ion concentration of the solution. The strong attractive force at high ion concentration gives rise to chain formation of the Janus particles, which can be explained by the quadrupolar charge distribution on the particles. Chain formation is observed irrespective of the direction of the self-propulsion of the particles. When both the position and the orientation of the heads of the chains are fixed, they exhibit beating behavior reminiscent of eukaryotic flagella. The beating frequency of the chains of Janus particles depends on the applied voltage and thus on the self-propulsive force. The scaling relation between the beating frequency and the self-propulsive force deviates from theoretical predictions made previously on active filaments. However, this discrepancy is resolved by assuming that the attractive interaction between the particles is mediated by the quadrupolar distribution of the induced charges, which gives indirect but convincing evidence on the mechanisms of the Janus particles. This signifies that the dependence between the propulsion mechanism and the interaction mechanism, which had been dismissed previously, can modify the dispersion relations of beating behaviors. In addition, hydrodynamic interaction within the chain, and its effect on propulsion speed, are discussed. These provide new insights into active filaments, such as optimal flagellar design for biological functions.
Highlights
IntroductionActive matter systems—collections of active elements that transduce free energy into motion—display a vast variety of intriguing nonequilibrium phenomena
We study the active dynamics of self-propelled asymmetrical colloidal particles (Janus particles) fueled by an AC electric field
Flagellar Dynamics of Chains of Active Janus Particles Fueled by an AC electric field17 there exist two characteristic frequencies for the velocity reversal and for the interaction switching
Summary
Active matter systems—collections of active elements that transduce free energy into motion—display a vast variety of intriguing nonequilibrium phenomena. Flagellar Dynamics of Chains of Active Janus Particles Fueled by an AC electric field collective motion of self-propelled particles interacting with each other has been intensively studied both theoretically and experimentally in the past few decades. The theoretical studies have predicted nontrivial properties such as giant density fluctuations in these globally ordered phases that contrast equilibrium systems, never have such properties been experimentally observed until very recently [4]. Interacting self-propelled Janus particles, driven by diffusiophoresis in a near-critical mixture [14] or fueled by hydrogen peroxide [15, 16], are reported to exhibit dynamical clusters or aggregates, where particles are constantly going in and out without forming strong connections between the particles
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