Disturbances electrokinetic

In active micromixer, pressure disturbance, electrohydrodynamic disturbance, dielec-trophoretic disturbance, electrokinetic disturbance, and magnetohydrodynamic disturbances are used to disturb the laminar streams (see Figure 4.13). The pressure pulse divides the... 

Sample preconcentration techniques are used with two purposes (1) to increase concentration in order to achieve detection and (2) to eliminate disturbances of the electrophoretic system during hydraulic or electrokinetic sample introduction when the conductivity of the sample is significantly different from that of the analysis buffer. It is important to keep sample manipulations and modifications to a minimum, and a rule of thumb is to prepare the sample so that its composition is at the same pH as the analysis buffer. It is also advantageous... 

In d.c. electrokinetics the time scale of the applied disturbance is usually much larger than that. The implication is that locally, in each segment of the double layer, the double layer may be considered at equilibrium, although over the particle as a whole, there is a tangential gradient in the ionic concentration. In sec. 3.13 we have referred to this feature as the local equilibrium principle. This principle starts to fail when the time scale of the applied disturbance is shorter than 10" s. For Instance, this may be the case in a.c. fields of frequencies 5 20 MHz. 

Figure 17.1. Schematic representation of an electrokinetic fence. Heavy metals and other polar contaminants are captmed in the electrolytes and periodically removed. There were no contamination downstream of the fence area and no disturbance of the groundwater flow...

In Fig. 5.15 the important in rheology shear plane, related to the electrokinetic potential, is indicated. It is the potential in the shear plane in relation to the potential of solntion, not disturbed by the presence of solid phase. A high potential C, value is typical for the dissipated colloidal suspension (sol) and the state of coagulation corresponds to the zero value of potential. This potential is reducing with the increasing degree of flocculation. 

Moreover, the ratio Rf a or hi a of the characteristic length scale of the medium to the discretization step determines the quality of the description of the geometry. Therefore, it affects equally the transport coefficients for uncharged solid walls and their disturbance by the electrokinetic effects. For example, the precision on a is bout 2-3 times (a/R), irrespective of the surface potential. 

Figure 7.9 Active micromixers (a) serial segmentation (b) pressure disturbance along mixing channel (c) integrated microstirrer in the mixing channel (d) electrohydrodynamic disturbance (e) dielectrophoretic disturbance (f) electrokinetic disturbance in a mixing chamber (g) electrokineticdisturbance in a mixing channel (h) thermal disturbance (i) combination of serial segmentation and focusing.

The term active mixer or active microimxef refers to a microfluidic device in which species mixing is enhanced by the application of some form of external energy disturbance. Typically, this disturbance is generated either by moving components within the micromixer itself, e.g. magnetically-actuated stirrers, or by the application of an external force field, e. g. pressure, ultrasound, acoustic, electrohydrodynamic, electrokinetic, dielectrophoretic, magneto-hydrodynamic, thermal, and so forth [1]. 

Figure 4.13 Schematic showing active mixing strategy (a) pressure disturbance leading to segmentation and (b) dielectrophoretic, electrohydrodynamic, electrokinetic, and magnetohydrodynamic disturbance generated by the electrode...

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