Electrostatics and Electrokinetics

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

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The thermophysical events in a can in the retort (dissolution, hydration, dehydration, gelatinization decrystallization, defibrillation, curling, uncurling, etc.) obviously must be complex. Charge superimposes electrostatic and electrokinetic reactions on the thermophysical processes. Broken-curve profiles for some polysaccharide foodstuffs manifest a transition from conduction to convection heating, as a tenuous, reversible suprastructure reverts to a liquefied mass under the influence of + A//mix. 

Imae, T., Electrostatic and electrokinetic properties of micelles, in Electrical Phenomena at Interfaces Fundamentals, Measurements, and Applications, 2nded., Ohshima, H. and Furusawa, K., Eds., Marcel Dekker, New York, 1998, chap. 28. 

Pujar, N. S., and Zydney, A. L. (1994). Electrostatic and electrokinetic interactions during protein transport through narrow pore membranes. Ind. Eng. Chem. Res. 33, 2473. 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

The examples shown is Section D indicate that the shape of calculated uptake curves (slope, ionic strength effect) can be to some degree adjusted by the choice of the model of specific adsorption (electrostatic position of the specifically adsorbed species and the number of protons released per one adsorbed cation or coadsorbed with one adsorbed anion) on the one hand, and by the choice of the model of primary surface charging on the other. Indeed, in some systems, models with one surface species involving only the surface site(s) and the specifically adsorbed ion successfully explain the experimental results. For example, Rietra et al. [103] interpreted uptake, proton stoichiometry and electrokinetic data for sulfate sorption on goethite in terms of one surface species, Monodentate character of this species is supported by the spectroscopic data and by the best-fit charge distribution (/si0,18, vide infra). 

The suppression of fhe removal rate of TaN film could nof be fully explained through the electrochemical phenomena by chemical reaction between complexing agent and the TaN film surface. We fhought that the TaN film loss and the Cu-to-TaN removal selectivity are directly related to the electrostatic interaction and electrokinetic behavior due to chemical adsorption and steric hindrance of adsorbed organic chemical. 

More generally speaking, when equilibrium is disrupted (in physics this constitutes the change from electrostatics to electrokinetics), a magnetic field is associated a priori with the electric field. These two fields are then described using the Maxwell equations. In electrochemistry, other than in exceptional cases , one can disregard the effects of magnetic field, and so in this scenario the electric field is derived from a potential, and therefore the Maxwell equations are reduced to the Poisson law ... 

Electrokinetics is essentially the consequence of a coupling between electrostatics and hydrodynamics. Newtonian hydrodynamics is widely assumed for the classic description of electrokinetics. However, practical applications of electrokinetics frequently deal with biofluids (such as solutions of DNA, blood, and protein, polymeric solutions, and colloid suspensions) which all are complex fluids and therefore demonstrate non-Newtonian behaviors. Recently intensive efforts on electrokinetics of non-Newtonian fluids have been made after Das and Chakraborty [1] who pioneered a theoretical analysis of electroosmosis of non-Newtonian fluids. Here in this entry the example of electroosmosis of non-Newtonian fluids in microchannels is used to demonstrate the fundamental formulation of non-Newtonian electrokinetics. 

In any of the electromechanical devices, strong electric fields act on the permanent or induced dipoles present along the polymeric chains promoting coulombic interactions, forcing conformational movements on the polymeric chains and concomitant macroscopic changes of volume, which relax in the absence of the electric field. Similar coulombic interactions occur when a solvent and ions are present, giving electrokinetic (electroosmotic and electrophoretic) processes. So, electrostatic and mechanical models applied to polymeric materials are required to model the attained responses. No chemical reaction is required for the actuation of those devices. 

In this chapter, we recall briefly some features of ionic transport in solutions [1]. Since the basic concepts of electrostatics and hydrodynamics have been presented before, we will directly present their application to electrokinetic phenomena after this first presentation. 

In the following sections, the relationship between surface charge and electrokinetic phenomena is expounded in terms of classical theory. First, a few possible mechanisms and models for the development of charge at a surface in contact with an aqueous solution are described in order to form a basis for the formation of an electrical double-layer at an interface. Secondly, the electrical double-layer is discussed in terms of an equilibrium charge distribution and electrostatic potential near the interface. With an adequate description of the interface, the discussion turns to explication of electrokinetic phenomena according to the charge distribution in the electrical double-layer and the Navier-Stokes equation. A section then follows which describes common methods and experimental requirements for the measurement of electrokinetic phenomena. The discussion closes with a few examples of the use of measurement of the pH dependence of electroosmosis as an analytical characterization technique from this present author s own experience. The intention is to provide... 

For hydrosols in gremular filtration, the external force consists of gravitational force, particle-collector surface interaction forces, such as the unretarded London attraction force (defined in (3.1.16)) and electrokinetic force (3.1.17) in the double layer, and electrostatic forces, if any, such as coulombic attraction/repulsion forces (3.1.15) (usually important in aerosol-removal processes unless the collector particles are deliberately charged). In... 

The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

Because stabilization in the Verwey and Hamaker picture is electrical, the use of electrical methods for predicting the stability of a dispersion appears to be mandatory. Other than the work of Voet described above, little has been done in this direction. Beyond doubt, the important developments in the area of dispersion stability that will come forth will be based either on electrokinetics (for high dielectric media, especially hydrocolloids) or electrostatics. 

The electrokinetic processes have electrostatic origins they are linked to the charges present on both sides of the slip plane close to the phase boundary. The charge and potential distribution in the surface layer can be described by the relations and laws outlined in Chapter 10. 

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