Dynamic Control of Speed and Trajectories of Active Droplets in a Nematic Environment by Electric Field and Focused Laser Beam

Rajabi, Mojtaba; Baza, Hend; Wang, Hao; Lavrentovich, Oleg D.

doi:10.3389/fphy.2021.752994

Cited by 6 publications

(4 citation statements)

References 36 publications

(53 reference statements)

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“…Correspondingly, droplet without bacteria exhibits no motion. Furthermore, the motion of the droplet can be guided by patterned nematic substrate, electric field, or focused laser beam [242].…”

Section: Migrating Active Dropletsmentioning

confidence: 99%

Bacterial active matter

Aranson¹

2022

Rep. Prog. Phys.

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Bacteria are among the oldest and most abundant species on Earth. Bacteria successfully colonize diverse habitats and play a signiﬁcant role in the oxygen, carbon, and nitrogen cycles. They also form human and animal microbiota and may become sources of pathogens and a cause of many infectious diseases. Suspensions of motile bacteria constitute one of the most studied examples of active matter: a broad class of non-equilibrium systems converting energy from the environment (e.g., chemical energy of the nutrient) into mechanical motion. Concentrated bacterial suspensions, often termed active ﬂuids, exhibit complex collective behavior, such as large-scale turbulent-like motion (so-called bacterial turbulence) and swarming. The activity of bacteria also aﬀects the eﬀective viscosity and diﬀusivity of the suspension. This work reports on the progress in bacterial active matter from the physics viewpoint. It covers the key experimental results, provides a critical assessment of major theoretical approaches, and addresses the eﬀects of visco-elasticity, liquid crystallinity, and external conﬁnement on collective behavior in bacterial suspensions.

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Section: Migrating Active Dropletsmentioning

confidence: 99%

Bacterial active matter

Aranson¹

2022

Rep. Prog. Phys.

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“…As already stated, the fore-aft director asymmetry enabling the active droplet's propulsion is caused by the surrounding far-field director of the liquid crystal medium. This far-field director can be designed as rectilinear or spatially and temporarily varied by several approaches, such as photopatterning of surface interactions 39 , application of the external electric field 16 , or by light irradiation, which allows one to control the propulsion direction. In the presented example, the photocontrol of the cholesteric pitch changes the inplane direction of active droplet propulsion, so that the control can be called two-dimensional.…”

Section: Discussionmentioning

confidence: 99%

“…As demonstrated previously, the trajectory of the active droplet could be controlled by surface patterning of the director 15 , by applying an electric field to realign the director, or by using a laser beam to locally melt the nematic into an isotropic phase 16 . These methods of control are either static (as in the case of photopatterning 15 ) or require a complicated design (such as patterned electrodes or precise focusing of the laser beam 16 ). There is thus a need to develop a method to dynamically control the trajectories of active droplets with a simpler design that can be applied from a distance.…”

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confidence: 97%

Dynamic control of active droplets using light-responsive chiral liquid crystal environment

Jirón,

Rajabi,

Wang

et al. 2024

Commun Phys

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Microscopic active droplets are of interest since they can be used to transport matter from one point to another. In this work, we demonstrate an approach to control the direction of active droplet propulsion by a photoresponsive cholesteric liquid crystal environment. The active droplet represents a water dispersion of bacterial Bacillus subtilis microswimmers. When placed in a cholesteric, a surfactant-stabilized active droplet distorts the local director field, producing a point defect-hedgehog, with fore-aft asymmetry, and allows for the chaotic motion of the bacteria inside the droplet to be rectified into directional motion. When the pitch of the cholesteric confined in a sandwich-like cell is altered by light irradiation, the droplet trajectory realigns along a new direction. The strategy allows for a non-contact dynamic control of active droplets trajectories and demonstrates the advantage of orientationally ordered media in control of active matter over their isotropic counterparts.

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“…13 As demonstrated previously, the trajectory of the active droplet could be controlled by surface patterning of the director, 13 by applying an electric field to realign the director, or by using a laser beam to locally melt the nematic into an isotropic phase. 14 These methods of control are either static (as in the case of photopatterning 13 ) or require a complicated design (such as patterned electrodes or precise focusing of the laser beam 14 ). There is thus a need to develop a method to dynamically control the trajectories of active droplets that does not require a complex design and can be applied from a distance.…”

Section: Introductionmentioning

confidence: 99%

Dynamic control of active droplets using light-responsive chiral liquid crystal environment

Lavrentovich,

Jiron,

Rajabi

et al. 2024

Preprint

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Microscopic active droplets are of interest since they can be used to transport matter from one point to another. The challenge is to control the trajectory. In this work, we demonstrate an approach to control the direction of active droplet propulsion by a photoresponsive cholesteric liquid crystal environment. The active droplet represents a water dispersion of bacterial B. subtilis microswimmers. When placed in a cholesteric, a surfactant-stabilized active droplet distorts the local director field, producing a point defect-hedgehog, which breaks the fore-aft symmetry. The chaotic motion of the bacteria inside the droplet is rectified into directional motion by the asymmetric director field outside the droplet. When the pitch of the cholesteric is altered by visible light irradiation, the asymmetry axis and thus the droplet trajectory realign along a new direction. Droplets realign counterclockwise on exposure to light of 535 nm, and clockwise on exposure to light of 450 nm, as dictated by the photoinduced change in the handedness of the cholesteric. The strategy allows for a non-contact dynamic control of active droplets trajectories and demonstrates the advantage of orientationally ordered media in control of active matter over their isotropic counterparts.

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Dynamic Control of Speed and Trajectories of Active Droplets in a Nematic Environment by Electric Field and Focused Laser Beam

Cited by 6 publications

References 36 publications

Bacterial active matter

Bacterial active matter

Dynamic control of active droplets using light-responsive chiral liquid crystal environment

Dynamic control of active droplets using light-responsive chiral liquid crystal environment

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