Electrokinetic Motion of Heterogeneous Particles

Another puzzling feature of ACEO is the strong decay of the flow with increasing salt concentration. For this reason, all experiments in the literature have used either very dilute solutions (mostly KCl) or water (deionized or from the tap). A few groups have studied the concentration dependence of ACEO in aqueous KCl solutions [3, 15, 16]. These experiments and recent work on electrokinetic motion of heterogeneous particles suggest that flows due to induced-charge electroosmosis exhibit... 

The electrokinetic motion of heterogeneous particles, having nonuniform composition and/or irregular shape, involves translation, rotation, and deformation due to the combined effects of electrophoresis, induced-charge electrophoresis, and dielectrophoresis. 

Electrokinetic Motion of Heterogeneous Particles, Fig. 1 Examples of unusual linear electrophoretic motion of heterogeneous particles, (a) A dumbhell consisting of two oppositely charged spheres connected by a rigid rod rotates to align as shown and moves in the direction of the electric field (positive mobility), even... 

Electrokinetic Motion of Heterogeneous Particles, Fig. 2 (a) Linear electrophoresis of a flexible, charged chain connected to a neutral bead in regimes of small, moderate, and large velocity as a model of end-labeled... 

Electrokinetic Motion of Heterogeneous Particles, Fig. 3 Induced-charge electrophoresis of Janus particles, illustrated for the case of metal partially coated with insulating thin films, fiom [9]. (a) Stable orientation in a uniform field, showing induced-charge and slip... 

Electrokinetic Motion of Heterogeneous Particles, Fig. 4 Experimental observation of ICEP of metallo-dielectric Janus particles in a uniform 10 kHz AC field, fi om [10], (a) Sequence of micrographs dcantnistrating motion transverse to the field in the direction of the dielectric (light) end propelled by the metallic (dark) end, where the velocity increases with the particle size as in Eq. 2. (b) Velocity versus field amplitude squared at difftaent bulk concentrations of NaCl... 

As illustrated by the examples above, the electrokinetic motion of heterogeneous particles is quite compUcated and relatively unexplored. From a theoretical point of view, there are many opportunities to discover new phenomena by further relaxing the nine assumptions listed at the beginning of this article. From an experimental point of view, much remains to be done to characterize the motion of heterogenous particles in electric fields, especially by ICEP and DEP at low frequency. 

Bazant and Squires recently predicted that polarizable particles in the bulk can undergo essentially arbitrary translatimi and/or rotation by ICEP in a uniform electric field, as long as they possess appropriate broken symmetries [2, 4], such as nmispherical shapes and/or nonuniform surface properties (e.g., due to coatings of different polarizability or compact-layer capacitance). The former cases begin to explain Murtsovkin s early observations and beg for new experiments to test a variety of specific theoretical predictions, discussed below. The latter cases, which had not previously been observed, are described in a companion article on electrokinetic motion of heterogeneous particles. 

Daghighi Y, Gao Y, Li D (2011) 3D mmuaical study of induced-charge electrokinetic motion of heterogeneous particle in a mitaochaimel. Electrochim Acta 56 4254 262... 

Much less attention has been paid to the electrokinetic motion of heterogeneous particles, which have non-spherical shape and/or non-uniform physical properties. By far the most theoretical work has addressed the case linear electrophoresis of non-polarizable particles with a fixed, equilibrium distribution of surface charge [1]. In that case, relaxing only assumption 2 leads to the classical prediction that the mobility of a particle of uniform composition (uniform zeta) is independent of the shape and size of the particle. Perhaps it was this insensitivity to geometry that led to the common belief that the electrophoretic mobility measures some kind of average surface charge, until the Anderson was the first to clearly point out that this is generally not the case [2]. By care-... 

Electrokinetic Motion of Heterogeneous Particles Electrokinetic Motion of Polarizable Particles Electroosmotic Row (DC)... 

---