Nonlinear Motion of Optically Torqued Nanorods

We apply light torques to single optically trapped glass nanorods suspended in water. The resulting motion is studied experimentally and consists of two distinct regimes: a linear regime where the rod angle increases linearly with time and a nonlinear regime where the rod angle changes nonlinearly, experiencing accelerations and rapid reversals. We present a detailed theoretical treatment for the motion of such nanorods, which agrees extremely well with the observed motion. The experiments are carried out so that the trapped and torqued nanorods move without influence from surfaces. Such a model system is critical to understanding the more complex motion that occurs near a surface. Studying such nonlinear motion both free of, and near, a surface is important for understanding nanofluidics and hydrodynamic motion at the nanoscale.