Organizing soft matter via chiral response

Atomic scale matter, like a particle with spin, can respond to external perturbations in a chiral way: the spin rotates in response to a magnetic field.  That is, a vector perturbation gives rise to an angular velocity.  The technology of pulsed nuclear magnetic resonance exploits this response to organize and manipulate a sample of initially disordered spins.  In this talk we explore the analogs of this principle in the world of colloidal matter—micron-scale solid bodies of irregular shape.  Such bodies can respond chirally to external forcing via their hydrodynamic coupling.  This chiral response is richer than that of a nuclear spin.  As with nuclear spin, this response gives a handle that can bring a randomly-oriented dispersion of colloidal objects into a common orientation.  The alignment can be created by phase locking, analogous to pulsed nuclear magnetic resonance.  It can also be created by random external perturbations.  Here the alignment principle is the phenomenon of “noise-induced synchronization” known in dynamical systems.