Fabrication and Electric Field-Driven Active Propulsion of Patchy Microellipsoids.

Jin Gyun Lee,Bhuvnesh Bharti,Kyle J M Bishop,Ahmed Al Harraq

doi:10.1021/acs.jpcb.1c01644

Jin Gyun Lee, Bhuvnesh Bharti + Show 2 more

Open Access

https://doi.org/10.1021/acs.jpcb.1c01644

Copy DOI

Abstract

Active colloids are a synthetic analogue of biological microorganisms that consume external energy to swim through viscous fluids. Such motion requires breaking the symmetry of the fluid flow in the vicinity of a particle; however, it is challenging to understand how surface and shape anisotropies of the colloid lead to a particular trajectory. Here, we attempt to deconvolute the effects of particle shape and surface anisotropy on the propulsion of model ellipsoids in alternating current (AC) electric fields. We first introduce a simple process for depositing metal patches of various shapes on the surfaces of ellipsoidal particles. We show that the shape of the metal patch is governed by the assembled structure of the ellipsoids on the substrate used for physical vapor deposition. Under high-frequency AC electric field, ellipsoids dispersed in water show linear, circular, and helical trajectories which depend on the shapes of the surface patches. We demonstrate that features of the helical trajectories such as the pitch and diameter can be tuned by varying the degree of patch asymmetry along the two primary axes of the ellipsoids, namely longitudinal and transverse. Our study reveals the role of patch shape on the trajectory of ellipsoidal particles propelled by induced charge electrophoresis. We develop heuristics based on patch asymmetries that can be used to design patchy particles with specified nonlinear trajectories.

Highlights

Swimming is a natural method for locomotion across many length-scales, ranging from fish to bacteria.[1]
The characteristics of the metal patch fabricated on ellipsoidal particles using metal vapor deposition are governed by their assembly on the substrate
Ellipsoidal particles can be partially shaded by neighboring particles during the metal vapor deposition, resulting in a wide variety of metal patch shapes on the ellipsoids

Summary

Introduction

Swimming is a natural method for locomotion across many length-scales, ranging from fish to bacteria.[1] Movement in fluids is governed by inertial and viscous forces acting on the swimmer; the ratio between these forces is characterized by the Reynolds number.[2] Locomotion of large organisms such as fish occurs at high Reynolds number where inertial effects override viscous forces.[3] In contrast, microorganisms swim at low Reynolds number where they cannot rely on inertial forces to move.[4] micron-sized swimmers in biological systems employ several different mechanisms of self-propulsion to navigate through complex environments.[5] Recent studies have begun to unravel the mechanisms of locomotion at the micron-scale, identifying correlations between the organism shape and its swimming trajectory.[6−8] For instance, C. crescentus, a bacterium widely found in fresh water lakes and streams, is known to swim along helical trajectories in threedimensions (3D) to enhance motility by tilting its body with respect to its rotating flagellar motor.[9,10] This enhanced motility is critical in the formation, growth, and survival of the bacterial colonies.[11]

Methods

Results

Conclusion