Correlation during solute diffusion

Although long-time Debye relaxation proceeds exponentially, short-time deviations are detectable which represent inertial effects (free rotation between collisions) as well as interparticle interaction during collisions. In Debye s limit the spectra have already collapsed and their Lorentzian centre has a width proportional to the rotational diffusion coefficient. In fact this result is model-independent. Only shape analysis of the far wings can discriminate between different models of molecular reorientation and explain the high-frequency pecularities of IR and FIR spectra (like Poley absorption). In the conclusion of Chapter 2 we attract the readers attention to the solution of the inverse problem which is the extraction of the angular momentum correlation function from optical spectra of liquids. 

An argument in favour of the correctness of the values of R calculated with the help of eqn. (26) is a correlation detected in ref. 28 between the values of R found in liquid solutions and the values of Rtatt 10 1 s found in solid solutions for the same acceptors (Fig. 25). Such a correlation must exist if the mechanism of electron transfer in either case is tunneling. The lower values of R, as compared with those of Rt, for the reactions of eaq and e(j with the same acceptor are accounted for in a natural way in terms of the tunneling mechanism by the difference of the characteristic times during which there occurs a tunneling. In liquids the characteristic time is the time of a diffusion jump at T = 300 K, 10 10 s, in solids, it is the time between the end of irradiation and the measurement of the radiation yield of et r, t 103s. 

The difficulty in analyzing the phase inversion process is due to the interactions between the three components involved, and to the complex diffusion and convective processes that play an important role during the membrane formation. However, many researchers agree that there are two dominating factors controlling the formation of phase inversion membranes thermodynamics and kinetics, correlated to each other during the solidification of casting solutions. 

In the last 5 years a lot of work has been done on modeling the osmotic dehydration process. Mostly, the theory of molecular diffusion in the solid has been used to predict the water loss during the process. An unsteady unidirectional diffusion described by the second Tick s equation was used to quantify the process by the effective diffusivity. The resulting diffusivity is generally correlated with the concentration and the temperature of the hypertonic solution [15-28]. 

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