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

Seventeen different commercially available barrier coatings were investigated using relaxation voltammetry (RV). From the analysis of the potential transients over a wide relaxation range, it is concluded that the whole relaxation procedure can be described by the superposition of three elementary processes: a charge transfer, a dielectric relaxation and a diffusion process. The detailed analysis of the mathematical properties of the dielectric relaxation contribution leads to a Williams–Watts like transfer function: φ( t)=2 exp[−( λt) β ]−exp[−2( λt) β ], where φ( t) is the normalised transient decay for pure dielectric relaxation, λ a macroscopic (reciprocal) time constant and β=0.5. A ‘two-step’ continuous time random walk mechanism is proposed for the dielectric relaxation process. Furthermore, it is shown that for the coatings under investigation an ‘ideal behaviour’ is more the rule than the exception.