Reorientation dynamics of microswimmers at fluid-fluid interfaces

Gidituri, Harinadha; Shen, Zaiyi; Würger, Aloïs; Lintuvuori, Juho S.

doi:10.1103/physrevfluids.7.l042001

Cited by 10 publications

(6 citation statements)

References 47 publications

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“…The SP method has been used to study the electrophoresis 41 , sedimentation 42 , and rheology of colloidal suspesions 43 , as well as the attachment of particles to bubble surfaces 35 , the capillary-induced bending of flexible fibres 36 , and the enhanced diffusion of swimming particles 44 , among others. For the specific case of squirmers at fluid-fluid interfaces considered here, our previous results for isoviscous systems 28 are in good quantitative agreement with the Lattice-Boltzmann simulations of Gidituri et al 26 , who studied the reorientation dynamics of squirmers trapped at the interface. Whenever comparison with experiments, analytical results, or alternative simulations, has been possible, SP results have shown excellent agreement (≲ 5 − 10%).…”

Section: B Smoothed Profile Methods For Binary Fluidssupporting

confidence: 89%

“…This type of viscotaxis is consistent with previous theoretical investigations on swimmers in viscosity gradients. 26,[46][47][48][49] These studies showed that a squirmer in a weak viscosity gradient will reorient in the direction of the lower viscosity region (negative viscotaxis), regardless of the swimming mode. This effect has been confirmed in experiments, such as the pullerlike alga Chlamydomonas reinhardtii, which was observed to accumulate in low-viscosity zones at sufficiently strong gradients [50][51][52][53][54] .…”

Section: Discussionmentioning

confidence: 95%

“…However, few theoretical studies have attempted to construct a general hydrodynamic description of microswimmers near (complex) fluid-fluid interfaces 18,[24][25][26] , i.e., near the boundaries between immiscible fluids. This may be due to the high computational costs associated with treating deformable and penetrable boundaries.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of microswimmers near a liquid–liquid interface with viscosity difference

et al. 2023

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Transport of material across liquid interfaces is ubiquitous for living cells and is also a crucial step in drug delivery and in many industrial processes. The fluids that are present on either side of the interfaces will usually have different viscosities. We present a physical model for the dynamics of microswimmers near a soft and penetrable interface that we solve using computer simulations of Navier–Stokes flows. The literature contains studies of similar isoviscous fluid systems, where the two fluids have the same viscosity. Here, we extend this to the more general case where they have different viscosities. In particular, we investigate the dynamics of swimmers approaching a fluid–fluid interface between phase-separated fluids with distinct viscosities. We find that the incoming angle, viscosity ratio, and swimming type (i.e., pusher, puller, or neutral) strongly influence the collision, resulting in four distinct dynamical modes: bouncing, sliding, penetrating, and hovering. The former three modes are also observed for isoviscous systems, while the hovering, in which strong pullers swim parallel to the interface at a non-zero distance, requires mismatched viscosities. Furthermore, swimmers exhibit a preference for lower viscosity fluids, known as viscotaxis. This implies that, for a wide distribution of contact angles, more swimmers will transition into the low-viscosity environment than vice versa. Consequently, a swimmer starting in a low-viscosity fluid is more likely to bounce back at the interface, while a swimmer in a high-viscosity fluid is more likely to penetrate the interface and enter the lower viscosity fluid.

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Section: B Smoothed Profile Methods For Binary Fluidssupporting

confidence: 89%

Section: Discussionmentioning

confidence: 95%

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Dynamics of microswimmers near a liquid–liquid interface with viscosity difference

et al. 2023

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“…We assume that the fluid viscosity is prescribed and steady, and not significantly disturbed by the presence and activity of the moving particle as in previous work [39][40][41] ; however, this is an uncontrolled approximation because we assume that the sharp gradient persists, nevertheless we will show that this reasonably captures the experimental observations 25 . We note that the viscosity gradients considered here are distinct from the long-lasting viscosity differences that can exist at the interface between immiscible fluids with non-negligible surface tension that can dramatically affect (and even prevent) the particle crossing [45][46][47][48] .…”

Section: A Model For Active Particles Crossing Sharp Viscosity Gradientsmentioning

confidence: 90%

Active particles crossing sharp viscosity gradients

Gong

Shaik

Elfring

2023

Sci Rep

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Active particles (living or synthetic) often move through inhomogeneous environments, such as gradients in light, heat or nutrient concentration, that can lead to directed motion (or taxis). Recent research has explored inhomogeneity in the rheological properties of a suspending fluid, in particular viscosity, as a mechanical (rather than biological) mechanism for taxis. Theoretical and experimental studies have shown that gradients in viscosity can lead to reorientation due to asymmetric viscous forces. In particular, recent experiments with Chlamydomonas Reinhardtii algae swimming across sharp viscosity gradients have observed that the microorganisms are redirected and scattered due to the viscosity change. Here we develop a simple theoretical model to explain these experiments. We model the swimmers as spherical squirmers and focus on small, but sharp, viscosity changes. We derive a law, analogous to Snell’s law of refraction, that governs the orientation of active particles in the presence of a viscosity interface. Theoretical predictions show good agreement with experiments and provide a mechanistic understanding of the observed reorientation process.

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“…Additionally, as the level of stratification intensifies, the separation angles between various swimmer types demonstrate divergent behaviors. Gidituri et al (2022) explored the orientation and translational mechanics of spherical squirmers trapped at fluid interfaces. Employing both numerical simulations and analytical calculations, they discovered that swimmers with weak dipole forces and strong puller characteristics align perpendicularly to the interface and eventually halt, whereas strong pushers tend to navigate along the interface toward areas of lower viscosity.…”

Section: Introductionmentioning

confidence: 99%

Motion characteristics of squirmers in linear shear flow

Guan,

Ying,

Lin

et al. 2024

Fluid Dyn. Res.

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In this study, the two-dimensional lattice Boltzmann method was employed to simulate the motions and distributions of a circular squirmer in a linear shear flow. The objective was to systematically investigate the dynamics of microorganisms or engineered squirmers in a flowing environment. We conducted multiple simulations across a range of self-propelled strengths (0.08 ≤ α ≤ 0.8) and squirmer type parameters (-5 ≤ β ≤ 5). Initially, we analyzed the swimming motions of the neutral squirmer (β = 0) in the shear flow. Our analysis revealed two distinct distributions depending on , i.e., near the bottom or the top plate, which differs from conventional particle behavior. Moreover, we observed that the separation point of these two distributions occurs at αc = 0.41. The puller and pusher exhibit similarities and differences, with both showing a periodic oscillation pattern (POP). Additionally, both types reach a steady inclined pattern near the plate (SIP), with the distinction that the low-pressure region of the puller's head is captured by the plate, whereas the pusher is captured by the low-pressure region on the side of the body. The limit cycle pattern (LCP) is unique to the pusher because the response of the pressure distribution around the pusher to the flow field is different from that of a puller. The pusher starts from the initial motion and asymptotes to a closed limit cycle under the influence of flow-solid interaction. The frequency f of LCP is inversely proportional to the amplitude h* because the pusher takes longer to complete a larger limit cycle. Finally, an open limit cycle is shown, representing a swimming pattern that crosses the width of the channel.

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Reorientation dynamics of microswimmers at fluid-fluid interfaces

Cited by 10 publications

References 47 publications

Dynamics of microswimmers near a liquid–liquid interface with viscosity difference

Dynamics of microswimmers near a liquid–liquid interface with viscosity difference

Active particles crossing sharp viscosity gradients

Motion characteristics of squirmers in linear shear flow

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