Chemically active filaments: analysis and extensions of slender phoretic theory

Katsamba, Panayiota; Butler, Matthew; Koens, Lyndon; Montenegro‐Johnson, Thomas D.

doi:10.1039/d2sm00942k

Cited by 4 publications

(1 citation statement)

References 31 publications

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“…Keller & Wu (1977) considered a spheroidal squirmer model, which was extended by later studies to probe the effect of geometrical shape upon ciliary locomotion (Ishimoto & Gaffney 2013;Theers et al 2016;Poehnl, Popescu & Uspal 2020). Furthermore, synthetic active particles of non-spherical shapes, including prolate spheroids and general slender bodies, were also fabricated and studied experimentally and theoretically (Champion & Mitragotri 2006;Champion, Katare & Mitragotri 2007;Glotzer & Solomon 2007;Shemi & Solomon 2018;Yariv 2019;Poehnl et al 2020;Poehnl & Uspal 2021;Katsamba et al 2022;Zhu & Zhu 2023). In particular, Poehnl et al (2020) analysed the self-diffusiophoretic motion of spheroidal particles in a Newtonian fluid.…”

Section: Introductionmentioning

confidence: 99%

Self-diffusiophoretic propulsion of a spheroidal particle in a shear-thinning fluid

Zhu,

van Gogh,

Zhu

et al. 2024

J. Fluid Mech.

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Shear-thinning viscosity is a non-Newtonian behaviour that active particles often encounter in biological fluids such as blood and mucus. The fundamental question of how this ubiquitous non-Newtonian rheology affects the propulsion of active particles has attracted substantial interest. In particular, spherical Janus particles driven by self-diffusiophoresis, a major physico-chemical propulsion mechanism of synthetic active particles, were shown to always swim slower in a shear-thinning fluid than in a Newtonian fluid. In this work, we move beyond the spherical limit to examine the effect of particle eccentricity on self-diffusiophoretic propulsion in a shear-thinning fluid. We use a combination of asymptotic analysis and numerical simulations to show that shear-thinning rheology can enhance self-diffusiophoretic propulsion of a spheroidal particle, in stark contrast to previous findings for the spherical case. A systematic characterization of the dependence of the propulsion speed on the particle's active surface coverage has also uncovered an intriguing feature associated with the propulsion speeds of a pair of complementarily coated particles not previously reported. Symmetry arguments are presented to elucidate how this new feature emerges as a combined effect of anisotropy of the spheroidal geometry and nonlinearity in fluid rheology.

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Section: Introductionmentioning

confidence: 99%

Self-diffusiophoretic propulsion of a spheroidal particle in a shear-thinning fluid

Zhu,

van Gogh,

Zhu

et al. 2024

J. Fluid Mech.

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Introduction to the Theories and Modelling of Active Colloids

Katsamba,

Montenegro-Johnson

2024

Active Colloids

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This chapter will introduce the mathematics of modelling of active (autophoretic) colloids. It is intended to be something of a beginners’ guide, rather than an extensive literature review, and hopefully has useful information for theorist and experimentalist alike. The focus will be on modelling active colloids at the particle level, rather than at the suspension level via coarse-grained continuum methods. We first take a particle-centered view, whereby we consider the forces acting on a single sphere, to get Langevin dynamics – an ordinary differential equation (ODE) for the Janus particle’s motion. We discuss how the dynamics of a collection of such particles can be simulated by solving these ODEs together, and about how to add in physics – such as pair-wise fluid interactions between particles – to make the modelling more realistic. We then switch viewpoints to focus on what is going on outside the particle in the fluid, looking at the partial differential equations that govern the interactions of the solute fuel, particle, and the propulsive flows. We discuss some numerical techniques for studying autophoretic systems within this framework, with a focus on the Boundary Element Method. We present a method of simplifying this framework for slender autophoretic filaments and loops with arbitrary 3D shape and chemical patterning. In doing so, we see that the particle viewpoint and the fluid viewpoint “meet in the middle”, as we describe the interacting particles as a set of fundamental solutions with increasingly fast decay – point sources, dipoles, forces, torques, and stresses. We finish with a discussion of some potential future directions.

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