Chemical relaxation methods wave absorption

Ultrasonic absorption is a so-called stationary method in which a periodic forcing function is used. The forcing function in this case is a sound wave of known frequency. Such a wave propagating through a medium creates a periodically varying pressure difference. (It may also produce a periodic temperature difference.) Now suppose that the system contains a chemical equilibrium that can respond to pressure differences [as a consequence of Eq. (4-28)]. If the sound wave frequency is much lower than I/t, the characteristic frequency of the chemical relaxation (t is the... 

Stationary relaxation methods include sound absorption und dlNpcrRlon and dielectric dispersion. A sound wave is used to perturb thc system (hat causes temperature and pressure alterations on an oscillating electric field. Then, chemical relaxation is measured by determining adsorbed energy (acoustical absorption or dielectric loss), or a phase lag that is dependent on the frequency of a forcing function (Bernasconi, 1986 Sparks, 1989). In this chapter, only transient relaxation methods will be discussed. 

The principle of the dielectric absorption relaxation technique is very similar to that of the ultrasonic relaxation. The coupling between electrical waves and the chemical equilibrium occurs through the change of dipole moment associated with the chemical reaction. The drawback of this method lies in its extreme sensitivity to all rotational motions occurring in the system and which all give rise to relaxation signals. The chemical contributions are then more difficult to extract and analyze. Nevertheless, the dielectric relaxation has been recently used for the study of the kinetics of processes occurring in systems of threadlike micelles. - ... 

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