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Abstract Self‐propelled colloids are primed to become scaled up, nano‐ and microscale inorganic analogues of molecular motors and machines. In order to advance toward the ambitious goal of employing such active particles to form genuine man‐made small scale machinery, a significantly diversified library of particle types, capable of a wide range of motive behaviors, must be available. Here, it is shown that the dynamics of photoactivated, self‐phoretic particles can be engineered by targeted design of metal–semiconductor heterojunctions. This effect is demonstrated with three different microswimmers consisting of an elongated semiconducting tail made from anatase titanium dioxide; all three of which would otherwise be identical absent vapor‐deposited coatings of gold at different locations on the tails. The specific location of the heterojunction determines the swimming behavior for each type. Although here only one shape and material combination is focused upon, engineering active particles with site‐specific metal–semiconductor heterojunctions is a general technique for achieving desired kinematic behavior in active colloidal matter.
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Alignment, Rising, Sticking, and Phototaxis: Modulating the Behavior of Hematite Micropeanuts
Abstract Artificial active colloids are an active area of research in the field of active matter and microrobotic systems. In particular, light‐driven semiconductor particles are shown to display interesting behaviors ranging from phototaxis (movement toward or away from a light source), rising from the substrate, interparticle attraction, attraction to the substrate, or other phenomena. However, these observations involve using multiple different designs of particles in varying conditions, making it unclear how the experimental parameters, such as pH, peroxide concentration, and light intensity, affect the outcomes. In this work, a peanut‐shaped hematite semiconductor particle is shown to exhibit a rich range of behavior as a function of the experimental conditions. The particles show rising, sticking, phototaxis, and in‐plane alignment of their long axes perpendicular to a magnetic field. A theoretical model accounting for gravity, van der Waals forces, electric double layer interactions with the glass surface, and self‐diffusiophoresis is formulated to describe the system. Using experimental data on the dependence of particle behavior on pH and ionic concentrations, the model captures the interplay of competing effects and explains many of the observed behaviors, providing insight into the relevant physical phenomena and how different environmental conditions can lead to such a rich diversity of behavior.
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- Award ID(s):
- 2234869
- PAR ID:
- 10565942
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 12
- Issue:
- 9
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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