Electrokinetic motion

The methods of measuring the velocity of electrokinetic motion are fully described in some of the reviews mentioned above. They include (for cataphoresis) various forms of U-tube in which the motion of the boundary of the suspension is observed, transference methods similar to Hittorf s transport number measurements in electrochemistry, and microscopic cells in which the motion of individual particles is watched, due allowance being made for the motion of the suspending fluid in the opposite direction to the particles. Sumner and Henry s device1 of fixing a sphere on a fibre and observing its deflexion in a horizontal electric field is very ingenious, and not so frequently mentioned as other methods. 

Electrokinetic Phenomena. Electrokinetic motion occurs when the mobile part of the electric double layer is sheared away from the inner layer... 

S. Park, A. Beskok, Alternating current electrokinetic motion of colloidal particles on interdigitated microelectrodes, Analytical Chemistry, 80(8) 2832-2841 (2008). 

Zeta Potential Strictly called the electrokinetic potential, the zeta potential refers to the potential drop across the mobile part of the electric double layer. Any species undergoing electrokinetic motion, such as electrophoresis, moves with a certain immobile part of the electric double layer that is assumed to be distinguished from the mobile part by a distinct plane, the shear plane. The zeta potential is the potential at that plane. 

Electrokinetic Phenomena. Electrokinetic motion occurs when the mobile part of the EDL is sheared away from the inner layer (charged surface). There are four types of electrokinetic measurements, electrophoresis, electroosmosis, streaming potential, and sedimentation potential, of which the first finds the most use in industrial practice. Good descriptions of practical experimental techniques in electrophoresis and their limitations can be found in references 18-20. 

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... 

Electrokinetic Motion of Polarizable Particles - Electroosmotic Flow (DC)... 

Daghighi Y, Li D (2011) Microvalve using induced-charge electrokinetic motion of Janus particle. Lab Chip 11 2929-2940... 

The dielectrophoretic particle motion, Udep > competes with the streamwise electrokinetic motion, Uek> leading to a cross-stream deflection ... 

Figure 3 shows the electrokinetic motion of 2.2 pm-diameter polystyrene particles in a 50 pm wide serpentine microchannel under the application of a DC-biased AC electric field [4]. When particles are suspended in 1 mM phosphate buffer, they experience negative DEP and are focused to a stream along the channel centerhne as demonstrated in Fig. 3 a. This is because particles are deflected from the inner to the outer comer when they pass the alternating turns and their equilibrium position is along the channel centerline [5, 6]. If, however, the C-iDEP is too strong, particles will bounce between the two sidewalls [7]. In contrast, when particles are suspended in pure water, they experience positive DEP and line the sidewalls of the serpentine microchannel as demonstrated in Fig. 3b. This is because particles are pulled into the inner comers of every single turn where the electric field is much greater than the outer comers. Such distinct focusing phenomena can be utilized to continuously sort particles by size in a serpentine microchannel [4].

Electrokinetic Motion of Cells and Nonpolarizable Particles, Fig. 1 Electrophoretic motion of a spherical particle... 

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. 

The electrokinetic motion of colloidal particles and molecules in solution in response to applied electric fields can be rather complicated, so many approximations have been made in theoretical treatments. The classical theory of electrophoresis, dating back over a century to Smoluchowski, considers homogeneous particles, which are ... 

Nonlinear electrokinetic phenomena, such as the electrokinetic motion of polarizable particles, have only been studied for a few decades, and attention is just begiiming to be paid to the nonlinear motion of heterogeneous particles due to induced-charge electrophoresis [7-9]. Recent theoretical work has relaxed assumptions 1-3, but much remains to be done. Surprising new possibilities include particles that rotate continuously or translate perpendicular to a uniform AC field [9]. 

---