Multigear Bubble Propulsion of Transient Micromotors.

Amir Nourhani,Fernando Soto,Joseph Wang,Emil Karshalev

doi:10.34133/2020/7823615

Amir Nourhani, Fernando Soto + Show 2 more

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https://doi.org/10.34133/2020/7823615

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Abstract

Transient, chemically powered micromotors are promising biocompatible engines for microrobots. We propose a framework to investigate in detail the dynamics and the underlying mechanisms of bubble propulsion for transient chemically powered micromotors. Our observations on the variations of the micromotor active material and geometry over its lifetime, from initial activation to the final inactive state, indicate different bubble growth and ejection mechanisms that occur stochastically, resulting in time-varying micromotor velocity. We identify three processes of bubble growth and ejection, and in analogy with macroscopic multigear machines, we call each process a gear. Gear 1 refers to bubbles that grow on the micromotor surface before detachment while in Gear 2 bubbles hop out of the micromotor. Gear 3 is similar in nature to Gear 2, but the bubbles are too small to contribute to micromotor motion. We study the characteristics of these gears in terms of bubble size and ejection time, and how they contribute to micromotor displacement. The ability to tailor the shell polarity and hence the bubble growth and ejection and the surrounding fluid flow is demonstrated. Such understanding of the complex multigear bubble propulsion of transient chemical micromotors should guide their future design principles and serve for fine tuning the performance of these micromotors.

Highlights

Micro/nanoscale motors, capable of efficient propulsion and complex operation, are at the forefront of research in microand nanotechnology and robotics [1]
A more detailed investigation of the effect of material selection upon multigear dynamics and discovering design principles for fine tuning the dynamics of multigear bubble propulsion micromotors will be the subject of our future studies
Our analysis of the fluid flow pattern around the microengines and its similarities to flow around filter feeder microorganisms suggest new possibilities aligned with our previous studies [33] for exploiting the transient micromotors for enhanced local mixing and environmental remediation

Summary

Introduction

Micro/nanoscale motors, capable of efficient propulsion and complex operation, are at the forefront of research in microand nanotechnology and robotics [1]. Bubble-propelled chemically powered autonomous micromotors—based on different designs, e.g., rockets or spheres—have been developed over the past decade to perform diverse tasks in biomedical, environmental, and industrial applications [2,3,4,5,6,7,8] External fields such as magnetic field have been employed to successfully guide and control the motion of micromotors [9]. The engines in the early generations of bubble-propelled micromotors employed catalytic degradation of fuels, such as hydrogen peroxide and sodium borohydride by materials such as platinum, palladium, or manganese oxide [10,11,12,13,14] While these micromotors offered proof of concept for microscale self-locomotion, their widespread use is restricted by the incompatibility of their fuels with biological environments. Another obstacle was the retrieval of the micromotor, made of nondegradable materials, upon completion of its task

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