Electric strength variability, electrical

Charged macromolecules, such as proteins or polymers, are often separated elec-trophoretically. The rate of migration through an electric field increases with net charge and field strength. Molecular size of analytes and viscosity of separation media both have inverse relationships with rate of migration. These variables must all be taken into account in order to optimize the conditions for an efficient electrophoretic separation. 

Perturbation or chemical relaxation techniques cause an equilibrium to be upset by a sudden change in an external variable such as temperature, pressure, or electric field strength. One then measures the readjustment of the equilibrium concentrations. The time resolution may be as short as 10 10 s, although 10 6 s is the limit more commonly attainable. The method requires no mixing, which is why its time resolution is so good. On the other hand, it is applicable only to equilibria that are properly poised under the conditions used. 

Chemical relaxation techniques were conceived and implemented by M. Eigen, who received the 1967 Nobel Prize in Chemistry for his work. In a relaxation measurement, one perturbs a previously established chemical equilibrium by a sudden change in a physical variable, such as temperature, pressure, or electric field strength. The experiment is carried out so that the time for the change to be applied is much shorter than that for the chemical reaction to shift to its new equilibrium position. That is to say, the alteration in the physical variable changes the equilibrium constant of the reaction. The concentrations then adjust to their values under the new condition of temperature, pressure, or electric field strength. 

Grain boundary defects are primarily responsible for the operation of zinc oxide (ZnO) varistors, a shortened form of variable resistor. The varistor behaves like an insulator or poor semiconductor at lower electrical field strengths, but at a critical breakdown voltage the resistance decreases enormously and the material behaves like an electrical conductor (Fig. 3.36). When a varistor is connected in parallel with electrical equipment, negligible power flows through it under normal low... 

Table 1.1 Conjugate pairs of variables in work terms for the fundamental equation for the internal energy U. Here/is force of elongation, Z is length in the direction of the force, <7 is surface tension, As is surface area, , is the electric potential of the phase containing species i, qi is the contribution of species i to the electric charge of a phase, E is electric field strength, p is the electric dipole moment of the system, B is magnetic field strength (magnetic flux density), and m is the magnetic moment of the system. The dots indicate scalar products of vectors.

Similar to HPLC and CE there are a number of important variables that affect the separation process in CEC. These include the electric field strength, mobile phase parameters, and stationary phase surface chemistry that are described as follows. 

The Helmholtz-von Smoluchowski equation indicates that under constant composition of the electrolyte solution, the EOF depends on the magnitude of the zeta potential, which is determined by various factors inhuencing the formation of the electric double layer, discussed above. Each of these factors depends on several variables, such as pH, specihc adsorption of ionic species in the compact region of the double layer, ionic strength, and temperature. 

PIEZOELECTRIC EFFECT. The interaction of mechanical and electrical stress-strain variables in a medium. Thus, compression of a crystal of quartz or Rochelle salt generates an electrostatic voltage across it, and conversely, application of an electric field may cause the ciystal to expand or contract in certain directions, Piezoelectricity is only possible in crystal classes which do not possess a center of symmetry. Unlike clcctrostricdon, the effect is lineal in the field strength. 

Equation 3.11 shows that the surface charge is directly related to the surface electrical potential ( j/0) and number of ion pairs per cubic centimeter (n) or ionic strength (/) Note that the only terms in Equation 3.6 that are variable are the valence and concentration of the ions in the bulk solution. In further dissecting Equation 3.6, one finds that under constant temperature, 8Jtne2z2/ K is a constant and can be defined as A. Therefore,... 

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