History hydrodynamic torque transitions in oscillatory spinning of stick-slip Janus particles

We theoretically investigate the oscillatory spinning of an axisymmetric stick-slip Janus particle (SSJP) under the creeping flow condition. Solving the unsteady Stokes equation together with a matched asymptotic boundary layer theory, we find that such a particle can display unusual viscous torque responses in the high frequency regime depending on the Stokes boundary layer thickness delta, the slip length lambda of the slip face, and the coverage of the stick face. Our analysis reveals that an SSJP will always experience a reduced Basset torque of 1/delta decay due to the presence of the slip face, with amplitude smaller than the no-slip counterpart irrespective of the value of lambda. If the coverage of the stick face is sufficiently small, the reduced Basset torque can turn into a constant torque plateau due to prevailing slip effects at larger values of delta, representing a new history torque transition prior to the slip-stick transition at delta similar to lambda. All these features are markedly different from those for no-slip and uniform slip particles, providing not only distinctive fingerprints for Janus particles but also a new means for manipulating these particles.