Viscoelasticity the high-frequency viscosity factorf

We study the behaviour in viscoelastic fluids of the high-frequency viscosity factor C(n(ωm)). This factor depends upon the number n(ωm) of exponential decay terms needed to describe the observed relaxation behaviour in a frequency range 0 to com. Quite generally n(ωm) increases with increasing ft)m and decreasing temperature (T). C can be interpreted as the ratio η(0)^fast/η(0)where η(0) is the zero frequency viscosity, and η(0)fast is that component of the viscosity that is associated with rapidly decaying relaxation processes, i.e. with processes that decay in times shorter than ω^-1. As T decreases, more relaxation processes become slow thereby accounting for a decrease in C; at sufficiently low T, the only fast processes are the very fast (molecular) ones that vary little with T and are called the ‘bare processes’. Thus at low T, C is small and varies as η^-1. At high T, 1-C can be associated with the shear-orientation parameter R, and at low T the quantity Cη(0)k²/ρ can be associated with the k dependent part of the shear wave relaxation frequency. © 1985 Taylor & Francis Group, LLC.