Fluid-induced propulsion of rigid particles in wormlike micellar solutions

Abstract

In the absence of inertia, a reciprocal swimmer achieves no net motion in a viscous Newtonian fluid. Here, using tracking methods and birefringence imaging, we investigate the ability of a reciprocally actuated particle to translate through a complex fluid that possesses a network. A geometrically polar particle, a rod with a bead on one end, is reciprocally rotated using magnetic fields. The particle is immersed in a wormlike micellar (WLM) solution that is known to be susceptible to the formation of shear bands and other localized structures due to shear-induced remodeling of its microstructure. Results show that the nonlinearities present in this WLM solution break time-reversal symmetry under certain conditions, and enable propulsion of an artificial “swimmer.” We find three regimes dependent on the Deborah number (De): net motion towards the bead-end of the particle at low De, net motion towards the rod-end of the particle at intermediate De, and no appreciable propulsion at high De. At low De, where the particle time scale is longer than the fluid relaxation time, we believe that propulsion is caused by an imbalance in the fluid first normal stress differences between the two ends of the particle (bead and rod). At De ∼ 1, however, we observe the emergence of a region of network anisotropy near the rod using birefringence imaging. This anisotropy suggests alignment of the micellar network, which is “locked in” due to the shorter time scale of the particle relative to the fluid.

Viscoelastic and elastomeric active matter: Linear instability and nonlinear dynamics

“…We hope our work will promote experiments on these and other forms of active viscoelastic matter; while the effects of viscoelasticity on individual swimmers have been studied previously [75,76], we are not aware of an equivalent study for bulk orientationally ordered phases. One related study did however consider the linear stability of the bulk isotropic phase in an Oldroyd-B fluid [18].…”

Active colloids in complex fluids

“…Perhaps the first experimental demonstration of elasticityenabled propulsion was provided by Arratia and co-workers [75,76]. In these experiments, an asymmetric particle (in this case a dimer) is actuated by an external magnetic field and it is forced to execute periodic reciprocal strokes, which results in no net motion in viscous Newtonian fluids.…”

“…However, powering self-propelling synthetic swimmers still remains a challenge [108]. Detailed experiments [75,76] demonstrate that driven artificial swimmers can move through complex fluids with only reciprocal actuations and a simple body shape. These synthetic externally-driven swimmers are appealing for biological applications since their propulsive mechanism is less complicated than alternate strategies.…”

Thrifty Swimming With Shear-Thinning: A Note on Out-of-Plane Effects for Undulatory Locomotion Through Shear-Thinning Fluids

“…Finally, sperm cells, which also use an undulatory swimming gait, move through viscoelastic and shear-thinning cervical mucus [5,7,13,28,33]. This biomedical relevance, improvements in analytical and numerical techniques, and recent experimental work towards using artificial [9,17,23] and biological propulsion [22,26] for disease detection and drug delivery has driven recent increased interest in modelling swimming at small length scales.…”