Micropropulsion and microrheology in complex fluids via symmetry breaking

TL;DR

This paper introduces a novel micro-propeller that exploits symmetry-breaking and non-Newtonian fluid properties to enable propulsion and rheological measurements in complex biological fluids.

Contribution

It combines symmetry-breaking design with nonlinear fluid dynamics to create a micro-propeller that can move in complex fluids and measure their rheological properties.

Findings

Propeller moves only in complex fluids with nonlinear behavior.

Derived expressions relate propulsion speed to fluid's normal stress coefficients.

Numerical and analytical models validate propulsion mechanism.

Abstract

Many biological fluids have polymeric microstructures and display non-Newtonian rheology. We take advantage of such nonlinear fluid behavior and combine it with geometrical symmetry-breaking to design a novel small-scale propeller able to move only in complex fluids. Its propulsion characteristics are explored numerically in an Oldroyd-B fluid for finite Deborah numbers while the small Deborah number limit is investigated analytically using a second-order fluid model. We then derive expressions relating the propulsion speed to the rheological properties of the complex fluid, allowing thus to infer the normal stress coefficients in the fluid from the locomotion of the propeller. Our simple mechanism can therefore be used either as a non-Newtonian micro-propeller or as a micro-rheometer.