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Active particles consume energy stored in the environment and convert it into mechanical motion. Many potential applications of these systems involve their flowing, extrusion, and deposition through channels and nozzles, such as targeted drug delivery and out‐of‐equilibrium self‐assembly. However, understanding their fundamental interactions with flow and boundaries remain incomplete. Herein, experimental and theoretical studies of hydrogen peroxide (H2O2) powered self‐propelled gold–platinum nanorods in parallel channels and nozzles are conducted. The behaviors of active (self‐propelled) and passive rods are systematically compared. It is found that most active rods self‐align with the flow streamlines in areas with high shear and exhibit rheotaxis (swimming against the flow). In contrast, passive rods continue moving unaffected until the flow rate is very high, at which point they also start showing some alignment. The experimental results are rationalized by computational modeling delineating activity and rod‐flow interactions. The obtained results provide insight into the manipulation and control of active particle flow and extrusion in complex geometries.
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Emergence of Ring‐Shaped Microstructures in Restricted Geometries Containing Self‐Propelled, Catalytic Janus Spheres
Abstract The evaporation of liquid droplets containing colloids is an omnipresent natural phenomenon that has received much attention due to the fundamental effects it entails, as well as the multitudes of fields in which it can be applied. The deposition of particulates onto a solid surface during evaporation tends to form ring‐like stains, which are a hallmark of the “coffee‐ring effect.” A wide variety of systems has already been employed to suppress or enable this effect, however, little attention has been focused on particles in restricted geometries that are driven far from equilibrium. Here, we investigate how self‐propelled, “active” catalytic Janus microspheres affect the ring stains left behind during the drying of a geometrically confined suspension containing such particles. Self‐propulsion results indirectly from the decomposition of hydrogen peroxide (H2O2) on the catalytically active hemispherical shell, while the diametrically opposite face is inert; this is how the system is driven out of equilibrium. The magnitude of activity can be controlled by adjusting the volume concentration of aqueous H2O2within the suspension. This parameter strongly influences the ring‐shaped microstructures obtained, especially when the concentration is sufficiently high to produce oxygen bubbles that take over the motion as opposed to auto‐phoresis.
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- Award ID(s):
- 1847670
- PAR ID:
- 10286518
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- ChemNanoMat
- Volume:
- 7
- Issue:
- 10
- ISSN:
- 2199-692X
- Format(s):
- Medium: X Size: p. 1125-1130
- Size(s):
- p. 1125-1130
- Sponsoring Org:
- National Science Foundation
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