(179ai) Spiral Boundaries Guiding Chemically Active Janus Particles

Previous experimental research studies have observed chemically active Janus particles being guided by a variety of geometric boundaries including straight walls, circular posts, ratchets, teardrops and the base of large colloidal spheres. Chemically active Janus particles were observed detaching from boundaries with sharp corners and circular posts of sufficiently high curvatures. Also, geometric solid boundaries have been designed to control the collective behavior of large batches of active colloids by guiding and collecting them into targeted areas.

Here their interaction with spiral boundaries of two curvature types is investigated with the goal to separate mixtures of active and inactive particles. Chemically active Janus particles, polystyrene beads with a thin platinum film on one hemisphere, are placed in an aqueous solution of hydrogen peroxide, where the platinum surface acts as a catalyst that decomposes hydrogen peroxide to water and oxygen on one side of the Janus particle. The reaction causes an oxygen gradient that propels the Janus particle forward. An observation cell is used to view the interaction of the particles with the PDMS spiral wall templates with Fibonacci and Archimedean designs.

In this talk, the swimming speeds of the active Janus particles will be reported as a function of the different curvatures of the spiral geometries. Further, the statistics will be reported from experiments conducted with mixtures of active and inactive particles to discern if separation of active and inactive particles occurs.