Colloidal Microswimmers with Eccentric Rotating Magnetic Fields

A novel micoscale swimmer can be generated by placing two paramagnetic colloids of different sizes in an eccentric rotating magnetic field.  For propulsion at the microscale, viscous forces dominate over inertial forces.  This results in the scallop theorem, where reversible displacements does not lead to any net motion.   To achieve controlled swimming at the microscale, the swimmer must be able to make a sequence of deformations that are cyclic but not time reversible.  Here we will describe a novel dynamical system where two paramagnetic bodies are placed in a circular eccentric rotating magnetic field.  They influence each other in such a manner that leads them to propel together in a directed manner.  The motion of each body tracks a half-moon course, shown in the figure below.  The series of images below show that the swimmer moves with a velocity of 40 microns/min.  Additionally we will show how stochastic forces enhance this novel method of propulsion.