Test of theory experimental studies

Exhaustive experimental studies on electrophoresis and sedimentation potential have been reported by Rastogi and Mishra [7] with a view to test the thermodynamic theory of the phenomena. The experimental setup involving (i) sedimentation column and (ii) optical assembly are shown in Figs. 6.1 and 6.2. Both sedimentation potential and electrophoretic velocity were measured with these setups. 

Experimental results show that for pyrex-water system L21 is constant, at least up to 150 V. On the other hand for pyrex-acetone system, Unear phenomenological relation is found to be valid up to 450 V. Onsager reciprocity relation was tested in each case and the results are given in Table 6.1 [7]. The results are in agreement with those of earlier workers [8]. 

In continuous systems, the situation is not so clear. On account of experimental difficulties, exhaustive tests as in the above case have not been performed. Nevertheless, experimental results on thermal diffusion and Dofour effect/Soret do support the theoretical predictions although in a much limited range, again on account of limited range of validity of Gibbs equation. 

The limitation of Gibbs equation and later efforts to extend the applicability through extended thermodynamics would be discussed in the appendices. 

Steady-state thermodynamics in the linear range provides a good glimpse of the non-equilibrium region close to equilibrium. The utility of steady-state thermodynamics is illustrated in the case of electro-kinetic phenomena in Parts Two and Three in the regions more and more distant from equilibrium (non-linear steady state, bistability, oscillations, pattern formation) including complexity and complex phenomena. 

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