Collective orientational dynamics of pinned chemically-propelled nanorotors

Abstract

Collections of chemically propelled nanomotors free to move in solution can form dynamic clusters with diverse properties as a result of interactions through hydrodynamic flow and concentration fields, as well as direct intermolecular interactions between motors. Here, we study the collective rotational behavior of pinned sphere-dimer motors where direct motor-motor interactions play no role. Since the centers of mass of the motors are pinned, they cannot execute directed translational motion, but they can pump fluid and rotate; thus, the rotors remain coupled through hydrodynamic and chemical fields. Using a microscopic simulation method that accounts for coupling through both these fields, we show that different rotor configurations with a high degree of correlation exist and their forms depend on the nature of the fluid-rotor interactions. The correlations are greatly reduced or completely destroyed when the chemical interactions are removed, indicating that hydrodynamic coupling, while present, plays a lesser role in determining the collective rotor dynamics. These conclusions are supported by Langevin dynamics simulations that neglect hydrodynamics and include an approximate form of coupling through chemical fields.

Review: Interactions of Active Colloids with Passive Tracers

“…Furthermore, assuming that the hydrodynamics are of a much shorter range than phoretic interactions [17], modeling the activity of the active particles as a constant velocity and creating a chemical sink field around the particles was shown [18]. Separate overdamped Langevin equations for active and passive tracers yield the positon of the passives, and besides emerging dynamics (gas-like, oscillating, and collapsing), the model captures well the decreasing speed of growing clusters observed experimentally [18].…”

Active rotational dynamics of a self-diffusiophoretic colloidal motor

“…The results provided in this paper should prove useful for such applications involving chemicallypowered diffusiophoretic motors. The concepts discussed here for active motor rotation are not restricted to spherical shapes and diffusiophoresis but are applicable to other geometries, such as sphere-dimer motors and other phoretic mechanisms, although detailed aspects of the description will require modification [21,27,32,54,55]. work was supported by Brain Pool Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (grant number: NRF-2019H1D3A2A02102052) and supported in part by the Natural Sciences and Engineering Research Council of Canada and Compute Canada.…”

Which interactions dominate in active colloids?

“…The MPCD method in turn has been used e.g. to explore hydrodynamic interactions in squirmers [234,235,298,299] and has also been generalized to account also for the chemical reaction dynamics at the surface of active colloids and to study the combined effects of phoretic and hydrodynamic interactions in self-diffusiophoretic colloids [260,300] as well as chemically powered nanomotors [262] and surface attached nanorotors [274]. Another simulation method which is frequently used to study the interactions between (spherical) active particles is the Stokesian dynamics method [301].…”

“…For active Janus colloids pinned on a substrate, ref. [274] has shown that the combined effect of hydrodynamic and phoretic interactions can lead to states with highly correlated particle orientations. Also in this work the phoretic interactions have been found to play the dominant role for the observed collective behavior.…”