Swimming Dynamics Near a Wall in a Weakly Elastic Fluid

We present a fully resolved solution of a low-Reynolds-number two-dimensional microswimmer in a weakly elastic fluid near a no-slip surface. The results illustrate that elastic properties of the background fluid dramatically alter the swimming hydrodynamics and, depending on the initial position and orientation of the microswimmer, its residence time near the surface can increase by an order of magnitude. Elasticity of the extracellular polymeric substance secreted by microorganisms can therefore enhance their adhesion rate. The dynamical system is examined through a phase portrait in the swimming orientation and distance from the wall for four types of self-propulsion mechanisms, namely: neutral swimmers, pullers, pushers, and stirrers. The time-reversibility of the phase portraits breaks down in the presence of polymeric materials. The elasticity of the fluid leads to the emergence of a limit cycle for pullers and pushers and the change in type of fixed points from center to unstable foci for a microswimmer adjacent to a no-slip boundary.