Chemistry Reference
In-Depth Information
Chapter 6
Swimming Droplets: Artificial Squirmers
Self-propelling droplets which closely mimic the locomotion of
some protozoal organisms, so-called squirmers, and their
hydrodynamic flow fields are presented.
6.1 Introduction
Self propelled particles (SPPs) typically carry their own energy and are not propelled
simply by the thermal buffeting due to the environment. As non-equilibrium entities,
they are not restricted to classical equilibrium constraints such as the fluctuation-
dissipation theorem and detailed balance. Consequently, SPPs are simple model
systems to study the behavior of non-equilibrium phenomena, in particular the
mechanics and statistics of active matter.
Studies on SPPs, motivated as it were by the quest for a description of living
phenomena, naturally began with the statistical mechanical aspects of biological
movement. Due to the relative theoretical and experimental convenience, focus has
been mainly on microscale cellular motility over other motion such as that of birds,
humans, animals etc. The predominance of viscous forces over inertial forces at
the microscopic scales (low Reynolds' numbers) simplifies theoretical treatment
due to linearity. However, due to time reversibility in the low Reynolds' number
regime, motionmechanisms can be quite complicated andmicrosopic organisms have
developed a variety of strategies to achieve locomotion that allow them to overcome
the viscous forces. Flagellated cells such as certain bacteria, sperm,
E. Coli
and
trypanosomes use nonreciprocal motions of their flagella to overcome viscous forces
and set themselves in motion [
1
-
4
]. Organisms such as cyanobacteria, paramecium,
