Dynamics of a microorganism in a sheared viscoelastic liquid

Abstract

In this paper, we investigate the dynamics of a model spherical microorganism, called squirmer, suspended in a viscoelastic fluid undergoing unconfined shear flow. The effect of the interplay of shear flow, fluid viscoelasticity, and self-propulsion on the orientational dynamics is addressed. In the limit of weak viscoelasticity, quantified by the Deborah number, an analytical expression for the squirmer angular velocity is derived by means of the generalized reciprocity theorem. Direct finite element simulations are carried out to study the squirmer dynamics at larger Deborah numbers. Our results show that the orientational dynamics of active microorganisms in a sheared viscoelastic fluid greatly differs from that observed in Newtonian suspensions. Fluid viscoelasticity leads to a drift of the particle orientation vector towards the vorticity axis or the flow-gradient plane depending on the Deborah number, the relative weight between the self-propulsion velocity and the flow characteristic velocity, and the type of swimming. Generally, pullers and pushers show an opposite equilibrium orientation. The results reported in the present paper could be helpful in designing devices where separation of microorganisms, based on their self-propulsion mechanism, is obtained.

Swimming with swirl in a viscoelastic fluid

“…Only recently have authors started to consider the effect of higher-order polar squirming modes (Datt etal. 2015; De Corato & D'Avino 2017; Pietrzyk etal. 2019) or the azimuthal squirming modes (Ghose & Adhikari 2014; Pak & Lauga 2014; Felderhof & Jones 2016; Pedley 2016; Pedley, Brumley & Goldstein 2016).…”

Squirmers with swirl at low Weissenberg number

“…Using this mathematical description of a micro-swimmer, researchers have leveraged both numerical simulations (Zhu et al. 2011, 2012; Li, Karimi & Ardekani 2014; De Corato & D'Avino 2017; Binagia et al. 2020) as well as asymptotic analysis (Lauga 2009; Yazdi, Ardekani & Borhan 2014, 2015; De Corato, Greco & Maffettone 2015; Datt et al.…”

Active Particles in Viscosity Gradients

“…In this work, we study viscotaxis using the classical spherical squirmer model [17][18][19]. Squirmers can be used to model different types of swimmers, from biological micro-organisms to diffusiophoretic Janus particles, within the same theoretical framework, and have been used in understanding swimming at small scales in both Newtonian (e.g., see [19] and references within) and non-Newtonian fluids (e.g., [20][21][22][23][24][25]). The squirmer model allows us to study the response of different classes of microwswimmers, namely, pushers, pullers and neutral swimmers, to spatial gradients in viscosity.…”