Induced‐charge electrophoresis of uncharged dielectric spherical Janus particles

Abstract

We derive the equations governing the dipolophoretic motion of an electrically inhomogeneous Janus particle composed of two hemispheres with differing permittivities. The general formulation is valid for any electric forcing, including alternating current (AC) and makes no assumptions regarding the size of the electric double layer (EDL). The solution is thus valid even for nanoparticles where the particle radius can be of the same order as the EDL thickness. Semi-analytic and numerical solutions for the linear phoretic velocity and angular rotation of a single Janus particle suspended in an infinite medium are given in the limit of uniform direct current (DC) electric forcing. It is determined that particle mobility is a function of the permittivity in each hemisphere and the contrast between them as well as the EDL length. For a particle in which both hemispheres are characterized by a finite permittivity, we discover that maximum mobility and rotation is not obtained in the Helmholtz-Smoluchowski thin EDL limit but is rather a function of the permittivity and EDL properties.

Alternating current induced-charge electrophoresis of leaky dielectric Janus particles

“…However, it is noted that in Ref. 26 we showed that (in the limit of dc forcing) the general trends observed for the velocity in the stable configuration were the same in the case of rotation. This correlation can also be extended to the case of ac electric forcing.…”

“…A rigorous derivation of the coefficients is given in Ref. 26 to yield the following two sets of coupled equations for n = 1, 2, 3. . .…”

“…The complex ratio between the permittivities of each hemisphere (dielectric contrast) is given by q(ω) = ε 2 (ω)/ε 1 (ω) and the symmetric matrices γ m, n and γ 1 m,n are given for any integerial values m, n by 25,26 …”

“…For more detail, the reader is referred to Ref. 26 wherein the dc solution is derived in depth. In Sec.…”

Pair interactions in induced charge electrophoresis of conducting cylinders

“…Harnett et al [37], and Wu and Li [34,35] reported that the ICEO can achieve an efficient mixing by positioning conducting triangle rods in the microchannel. Furthermore, fluid pumping [38][39][40] and particle manipulation [41][42][43] are also realizable when the ICEO flow is asymmetric.…”