Run-and-halt motility of droplets in response to light

doi:10.1016/j.chempr.2022.06.017

Chem

Volume 8, Issue 8, 11 August 2022, Pages 2290-2300

https://doi.org/10.1016/j.chempr.2022.06.017 Get rights and content

Under a Creative Commons license

open access

Highlights

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Molecular photoswitches mediate the motility of droplets
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Photoactive micelles formed by molecular switches fuel droplet motion
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Photoactive micelles gate motility in response to light
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Droplets evolve motile patterns such as run-and-halt and photokinetic motion

The bigger picture

From the swim of bacteria to the beat of a heart, macroscopic movement is a hallmark of life and is ultimately driven by molecular machines. Artificial molecular machines display sophisticated motion with the potential to be harnessed into the purposeful movement of compartments. However, our perception of macroscopic movement differs from the rules that govern movement at the molecular scale. Large-scale functional movement can only emerge when molecular chemistry is coupled to physical processes that operate at larger length scales. We show that the geometry of the amphiphilic switches (molecular level) determines the geometry of micelles (supramolecular level), which in turn determines whether droplet movement can emerge (ensemble level). Eventually, the droplets display motile patterns reminiscent of those of swimming cells. We conclude that molecular behavior can be related to droplet motility rationally, which is a prerequisite for the design of functional motile systems.

Summary

Microscopic motility is a property that emerges from systems of interacting molecules. Unraveling the mechanisms underlying such motion requires coupling the chemistry of molecules with physical processes that operate at larger length scales. Here, we show that photoactive micelles composed of molecular switches gate the autonomous motion of oil droplets in water. These micelles switch from large trans-micelles to smaller cis-micelles in response to light, and only the trans-micelles are effective fuel for the motion. Ultimately, it is this light that controls the movement of the droplets via the photochemistry of the molecules composing the micelles used as fuel. Notably, the droplets evolve positive photokinetic movement, and in patchy light environments, they preferentially move toward peripheral areas as a result of the difference in illumination conditions at the periphery. Our findings demonstrate that engineering the interplay between molecular photo-chemistry and microscopic motility allows designing motile systems rationally.

Graphical abstract

Keywords

artificial molecular switches

motility

systems chemistry

light

liquid crystals

UN Sustainable Development Goals

SDG7: Affordable and clean energy

Data and code availability

The script for motile droplets tracking is available on request.

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²: Lead contact