Tubular catalytic micromotors in transition from unidirectional bubble sequences to more complex bidirectional motion

Abstract

The generation of oxygen microbubbles in catalytic microtubes has attracted tremendous attention towards the exploration of unidirectional and overloaded bubble ejection regimes, leading to simple and more complex motions of micromotors. While it is widely believed that a bubble's frequency in a unidirectional regime (i.e., a bubble ejected from a single tubular opening) is random, this study shall demonstrate that periodic oxygen bubble frequencies and sequences can be experimentally controlled using various concentrations of hydrogen peroxide fuel and surfactants. When released from a substrate, unidirectional micromotors self-propel in straight, circular, and helical trajectories, leading to a class of well-predictable or simple micromachines. Under overloaded conditions, micromotors generate bubbles at both tubular openings, which influence the trajectories of micromotor motion strongly. A one-dimensional reaction-diffusion equation is formulated to explain the possible mechanisms of mass transport in microtubes and the transition from the unidirectional to the overloaded regime of micromotors.

Parameters Optimization of Catalytic Tubular Nanomembrane-Based Oxygen Microbubble Generator

“…Previously reported fabrication process of rolled-up catalytic microtubes were used to synthesize the Ti/Cr/Pd tubes [ 23 , 29 , 42 ]. A photoresist ARP-3510 was deposited on 1-inch square Si (100) wafer by the spin coating method at 3500 rmp for 35 s and soft baked at 90 °C for 2 min.…”

“…Subsequently, different catalysts (e.g., Ag) [ 20 ], fabrication methods (e.g., template electrosynthesis) [ 21 ] and tubular wall materials (e.g., graphene/MnO 2 [ 22 ]) have been investigated. It is worthy to note that microtubes can produce bubbles from a single tubular opening (unidirectional regime) or both tubular openings (“overloaded”, bidirectional regime) [ 23 ]. Novel microfluidic techniques based on glass capillaries have been adopted to produce nanoparticle-shelled bubbles with catalytic shells [ 24 ].…”

Magnetic Nanomotor-Based Maneuverable SERS Probe

“…Micro-/nanomotors (MNMs) are miniaturized architectures or devices that can convert other forms of energy in the surrounding environment into mechanical motion in fluid [1,2]. They can be powered by harnessing internal energy released from chemical reactions (e.g., catalytic reactions or enzymatic reactions) [3][4][5][6][7][8], obtaining kinetic energy converted from external physical fields (e.g., magnetic, acoustic, optical and electrical field) [9][10][11][12][13], or getting the aid from biological organisms [14][15][16]. Taking advantage of their movement at a small scale, MNMs have demonstrated revolutionary applications as functional micro-/nanorobots undertaking on-demand tasks such as targeted drug delivery [17][18][19][20], microsurgery [8,21,22], and environmental remediation [23][24][25].…”

Catalytic/magnetic assemblies of rolled-up tubular nanomembrane-based micromotors

“…Previously, it was determined that the tubular aspect ratio is a crucial parameter for both activations of tubes in unidirectional (i.e., ejection of O 2 bubbles) and overloaded regimes (generation of bubbles from both tubular openings) [26][27][28]. Fig.…”