Catalytic Microtubular Jet Engines Self‐Propelled by Accumulated Gas Bubbles

Abstract

Strain-engineered microtubes with an inner catalytic surface serve as self-propelled microjet engines with speeds of up to approximately 2 mm s(-1) (approximately 50 body lengths per second). The motion of the microjets is caused by gas bubbles ejecting from one opening of the tube, and the velocity can be well approximated by the product of the bubble radius and the bubble ejection frequency. Trajectories of various different geometries are well visualized by long microbubble tails. If a magnetic layer is integrated into the wall of the microjet engine, we can control and localize the trajectories by applying external rotating magnetic fields. Fluid (i.e., fuel) pumping through the microtubes is revealed and directly clarifies the working principle of the catalytic microjet engines.

Electrodeposited conductive polymers for controlled drug release: polypyrrole

“…The movements of positively charged ions create an electroosmotic flow on the nanorods/liquid interface and drag the electrolyte solution by viscosity forces, thus causing the movements of nanorods in the reverse direction by speeds that are up to ≈40 μm s −1 [71,73]. In addition, other proposed catalytic nanomotors have used different propulsion methods, such as self-diffusiophoresis (spontaneous motion of dispersed particles in a fluid induced by a concentration gradient) [75] and bubble ejection [76]. Moreover, these miniature devices can be propelled and controlled by external stimulation, such as magnetic fields [77,78], external electric fields [79], visible light [80], ultraviolet light [81] and ultrasonic energy [82,83].…”

A Pickering Emulsion Route to Swimming Active Janus Colloids

“…However, despite this attention, the current methods by which synthetic catalytic swimming devices are manufactured remain cumbersome and have significant drawbacks, which limit the viability of proposed applications, and prevent extensive experimental research effort into active colloid phenomena. Prominent, widely studied examples of synthetic swimming devices include bimetallic rods, consisting of connected catalytically active and inactive segments,8 microrockets, consisting of rolled‐up microtubes with catalyst coating the interior walls,9 and Janus particles, consisting of spherical colloids where one hemisphere is catalytically active 10. Platinum is used as the catalytically active material in the majority of the reported examples due to its ability to perform the rapid room‐temperature decomposition of hydrogen peroxide, and consequently produce motion via either phoretic11 or bubble release mechanisms 12.…”

Mini and Micro Propulsion for Medical Swimmers

“…The micro robots that harness natural organisms or use the artificial cilia/flagella (regardless of motion types, corkscrew motion, or flexible oar motion) generate propulsion via viscous stress interaction [17,18,[21][22][23][24][25][26]. Among the chemical micro swimmers, even though there are still debates on the mechanism [27], some devices utilize the bubble recoiling method to make momentum transfer by inertia propulsion [28][29][30][31]. The electric and thermophoresis methods may be categorized as viscous propulsion, as the active Brownian motion method may [32][33][34][35].…”

“…Solovev et al [30] developed a micro tubular jet using a multi-metallic film. The film had a platinum inner layer used for decomposing the hydrogen peroxide and a ferromagnetic layer for the magnetic direction control, as shown in Figure 8b.…”