Electro-Orientation and Electro-Rotation of Metallodielectric Janus Particles.

The electro-rotation (EROT) and electro-orientation (EOR) behavior of metallodielectric spherical Janus particles (JP) are studied analytically and verified experimentally. This stands in contrast to previous either heuristic or numerically computed models of JP dipoles. First, we obtain frequency-dependent analytic expressions for the corresponding dipole terms for a JP composed of dielectric and metallic hemispheres by applying the "standard" (weak-field) electrokinetic model and using a Fourier-Legendre collocation method for solving two sets of linear equations. EROT and EOR spectra, describing the variation of the JP's angular velocity on the forcing frequency of a rotating and nonrotating spatially uniform electric field, respectively, are explicitly determined and compared against experiments (different JP sizes and solution conductivities). While a favorably good agreement between theory and experimental measurements was found for the frequency response (∼8% difference), there is still a factor of ∼2 difference in the amplitude of the angular velocity, which necessitates further future improvements to the model.