Free Surface Electrokinetics

Free surface electrokinetics Interfacial electrohydrodynamics Free surface electrohydrodynamics... 

In most electroosmotic flows in microchannels, the flow rates are very small (e.g., 0.1 pL/min.) and the size of the microchannels is very small (e.g., 10 100 jm), it is extremely difficult to measure directly the flow rate or velocity of the electroosmotic flow in microchannels. To study liquid flow in microchannels, various microflow visualization methods have evolved. Micro particle image velocimetry (microPIV) is a method that was adapted from well-developed PIV techniques for flows in macro-sized systems [18-22]. In the microPIV technique, the fluid motion is inferred from the motion of sub-micron tracer particles. To eliminate the effect of Brownian motion, temporal or spatial averaging must be employed. Particle affinities for other particles, channel walls, and free surfaces must also be considered. In electrokinetic flows, the electrophoretic motion of the tracer particles (relative to the bulk flow) is an additional consideration that must be taken. These are the disadvantages of the microPIV technique. 

In addition to the usual mathematical difficulties associated with free surface problems, the consideration of free surfaces becomes extremely important in microfluidics, especially given the increasing dominance of surface forces over body forces as the surface area to volume ratio increases with miniaturization. In addition, the curvature of the free surface becomes commensurate with the characteristic length scale of the system at these small scales. For example, the bubbles generated due to electrode reactions in electrokinetic microdevices can have dimensions which are on the same order as the microchannel width or height. 

The term interfacial electrokinetic flow here enconpasses all electrokinetically driven flows involving free-surfaces or freely deforming boundaries, i. e., gas-liquid interfaces or immiscible liquid-liquid interfaces. 

Certain organic molecules, e.g. 7,7,8,8,-tetracyanoquinodimethane TCNQ can accept electrons and form free anion radicals stable at room temperature. Concentrations of TCNQ and TCNQ radical can be determined using ESR, or even assessed on the basis of coloration. Meguro and Esumi [345] proposed a method to determine acid base properties of solid surfaces from radical concentration in the surface layer for a series of electron acceptors having different electron affinities. In this method a tacit assumption is made that except for the studied absorbent and TCNQ/TCNQ radical there are no other electron acceptors or donors in the system, which is not necessarily correct. This problem is analogous to assessment of acid base properties of materials based on their electrokinetic potentials in allegedly pure organic solvents (Section V). 

Adsorption of enteric viruses on mineral surfaces in soil and aquatic environments is well recognized as an important mechanism controlling virus dissemination in natural systems. The adsorption of poliovirus type 1, strain LSc2ab, on oxide surfaces was studied from the standpoint of equilibrium thermodynamics. Mass-action free energies are found to agree with potentials evaluated from the DLVO-Lifshitz theory of colloid stability, the sum of electrodynamic van der Waals potentials and electrostatic double-layer interactions. The effects of pH and ionic strength as well as electrokinetic and dielectric properties of system components are developed from the model in the context of virus adsorption in extra-host systems. 

We examined in our experiments the factors that influence electrokinetic cleaning of different clay grounds (from sandy loam to clay) from radioactive nuclides containing isotopes of °Sr, Sr, Cs, Cs, and so on. Of them, isotopes of °Sr and Cs are the most biologically harmful, having half-value periods of 28 and 30 years, respectively. These and other radioactive isotopes are present in both free (dissolved) and sorbed forms on particle surfaces (Cornell, 1993). 

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