Dielectric relaxation in barrier coatings: A square root of time process

Seventeen different commercially available barrier coatings were investigat ed using relaxation voltammetry (RV). From the analysis of the potential tr ansients over a wide relaxation range, it is concluded that the whole relax ation procedure can be described by the superposition of three elementary p rocesses: a charge transfer, a dielectric relaxation and a diffusion proces s. The detailed analysis of the mathematical properties of the dielectric r elaxation contribution leads to a Williams-Watts like transfer function: ph i(t)=2 exp[-(lambda t)(beta)]-exp[-2(lambda t)(beta)], where phi(t) is the normalised transient decay for pure dielectric relaxation, lambda a macrosc opic (reciprocal) time constant and beta=0.5. A 'two-step' continuous time random walk mechanism is proposed for the dielectric relaxation process. Fu rthermore, it is shown that for the coatings under investigation an 'ideal behaviour' is more the rule than the exception. (C) 2000 Elsevier Science S .A. All rights reserved.