Transition from Linear to Circular Motion in Active Spherical-Cap Colloids

Nonspherical
self-propelling colloidal particles offer many possibilities for creating
a variety of active motions. In this work, we report on the transition
from linear to circular motion of active spherical-cap particles near
a substrate. Self-propulsion is induced by self-diffusiophoresis by
catalytic decomposition of hydrogen peroxide (H2O2) on one side of the particle. Asymmetric distribution of reaction
products combined with the asymmetric shape of the particle gives
rise to two types of motions depending upon the relative orientation
of the particle with respect to the underlying substrate. At a low
concentration of H2O2, linear active motion
is observed, whereas increasing the H2O2 concentration
leads to persistent circular motion. However, the speed of self-propulsion
is nearly independent of the size of the particle. The study demonstrates
the use of nonspherical particles to create linear and circular motion
by varying the fuel concentration.