Chemically Propelled Motors Navigate Chemical Patterns

Abstract

Very small synthetic motors that use chemical reactions to drive their motion are being studied widely because of their potential applications, which often involve active transport and dynamics on nanoscales. Like biological molecular machines, they must be able to perform their tasks in complex, highly fluctuating environments that can form chemical patterns with diverse structures. Motors in such systems can actively assemble into dynamic clusters and other unique nonequilibrium states. It is shown how chemical patterns with small characteristic dimensions may be utilized to suppress rotational Brownian motions of motors and guide them to move along prescribed paths, properties that can be exploited in applications. In systems with larger pattern length scales, domains can serve as catch basins for motors through chemotactic effects. The resulting collective motor dynamics in such confining domains can be used to explore new aspects of active particle collective dynamics or promote specific types of active self‐assembly. More generally, when chemically self‐propelled motors operate in far‐from‐equilibrium active chemical media the variety of possible phenomena and the scope of their potential applications are substantially increased.

Pairing, waltzing and scattering of chemotactic active colloids

“…The roles of hydrodynamic flow [18][19][20][21][22][23][24], diffused solute [25][26][27][28][29], local phase change [30] and optical shadowing [31,32] as mediators of these interactions have been studied, as well as guidance by nearby boundaries [33][34][35]. Unravelling the dependence of phoretic and chemotactic effects on the surface profiles of catalyst concentration and solute-colloid interaction [8,[36][37][38] and symmetry-based classifications of pair interactions [39] have opened up the possibility of engineering active colloids with desired behaviour [40,41]. We also note that time-periodic behaviours arising through the momentum-like role of the polar orientation [19,[42][43][44] have been observed in thermophoretic colloids in a diverging source of light [45] as well as in paramecium with multiple flagellated protrusions [46].…”

Directed assembly of active colloidal molecules

“…The minimal distance between particles that attract each other is of order l 0 , therefore fixing the hard-core diameter. For comparison, in the experiments described in [25], l 0 ≈10 μm and v 0 ≈1 μm s −1 , resulting in t 0 ≈1 s. Similar molecules have been found with different choices of the mobilities' signs [25,26,32] but we are not aware that the oscillating chain can be formed like that, so we restrict ourselves to the present case.…”

“…In [32], it was shown that Janus particles can be guided in chemical landscapes. Here, we show that the same is possible in self-assembled colloids, with the precaution that the chemical gradient should not break the colloidal molecules apart.…”

Simulation of microswimmer hydrodynamics with multiparticle collision dynamics*

“…When active sphere dimers are pinned on a 2D layer but free to rotate, strong orientational correlations exist, mainly induced by chemical interactions [92]. If the background medium is chemically inhomogeneous, chemically active microswimmers are able to react to local gradients, or even follow chemical patterns [93]. Time-periodic oscillations of the chemical background medium leads to a periodic dispersion-aggregation transition of active nano-dimers [94].…”