Multiple representation of linear dielectric response

Abstract

Within the linear stimulus-response framework, dielectric responses of materials can be described in a dual way in terms of the complex dielectric constant ε*(ω) and complex dielectric modulus M*(ω) (= 1/ε *(ω)), both being defined as functions of angular frequency ω. In a phenomenological sense, ε*(ω) and M*(ω) are completely equivalent to each other. In this sense, a characteristic dielectric relaxation time τ can be defined for either quantity. However, in many cases, τ directly reflecting a slow molecular process(es) underlying the dielectric relaxation is defined for ε*(ω) but not for M*(ω), which is similar to the situation for the viscoelastic modulus and compliance, G*(ω) and J*(ω), the former often serving as the fundamental quantity detecting the slow molecular process. Focusing on some examples, this article discusses the duality in the representation of the dielectric responses and the superiority of ε*(ω) compared to M*(ω). © 2010 The Society of Rheology, Japan.