Self-propulsion of a freely-suspended, rotationally-symmetric swimmer enabled by viscoelastic normal stresses, Part II: Experiment

Building upon theoretical results describing a novel swimmer consisting of counter-rotating symmetric objects (Part I), here we present a physical implementation as an untethered robot capable of propulsion at low Reynolds number, only when submerged in a non-Newtonian fluid. This optically controlled, battery-powered robot propels itself in the direction of  the larger “head”.  We directly compare the experimental performance of this swimmer to theoretical and numerical predictions. Variations in the geometry of the robot are explored (tail sizes, shapes) to optimize the forward propulsion speed. By controlling the relative rotation rate while recording motility, we propose a novel application of this robot to function as a rheological probe of its local surrounding fluid. We assess the accuracy and limitations of such an approach in several fluids, by comparing the measured primary normal elastic stress to measurements taken with a standard benchtop rheometer. This proof-of-concept device experimentally demonstrates that a unique propulsion mechanism exists for elastic, non-Newtonian fluids.

 

(See: “Self-propulsion of a freely-suspended, rotationally-symmetric swimmer enabled by viscoelastic normal stresses, Part I: Theory and simulation”, presented by co-author J.P. Binagia).