The dynamics of microswimmers moving inside a drop of viscous liquid depends on many things, including the shape and size of the drop, the number of microswimmers and the Reynolds number of the liquid. This is a measure of viscosity; liquids with low Reynolds number are more viscous and flow in a linear manner with little turbulence. The flow of such a liquid can be modelled by solving a set of partial differential equations known as the Navier-Stokes equations. In this case, the microswimmer itself was considered as a force dipole confined within the drop and located at a set point. The presence of a layer of surfactant surrounding the drop containing the microswimmer was modelled using boundary conditions.

Solving these equations in a range of conditions -- drops with or without surfactant coats, stationary and freely moving, and with different Reynolds numbers and radii -- gave Daddi-Moussa-Ider and his co-workers a set of subtly different flow fields, from which the dynamics of the microswimmer could be defined. They note that these models of swimmer dynamics may prove useful in designing micro-machines for materials assembly, biosensing and micro-surgery as well as drug delivery.

Story Source:

Materials provided by Springer. Note: Content may be edited for style and length.

Journal Reference:

1. Alexander R. Sprenger, Vaseem A. Shaik, Arezoo M. Ardekani, Maciej Lisicki, Arnold J. T. M. Mathijssen, Francisca Guzmán-Lastra, Hartmut Löwen, Andreas M. Menzel, Abdallah Daddi-Moussa-Ider. Towards an analytical description of active microswimmers in clean and in surfactant-covered drops. The European Physical Journal E, 2020; 43 (9) DOI: 10.1140/epje/i2020-11980-9