Analysis of the Linear Viscoelastic Relaxation of a Liquid Hydrocarbon

Measurements have been made of the real part of the shear impedance of pure 2,2,4,4,6,8,8-heptamethylnonane at frequencies of 6, 18, 30, and 78 MHz at temperatures between − 132° and − 79°C. The viscosity at zero rate of shear, ρ(0), was also measured down to − 95°C and extrapolated to the lower temperatures. Analysis of the results depends critically on having values of ρ(0) and the limiting shear compliance at infinite frequency, J(∞). New extrapolation techniques are introduced for obtaining J(∞) in the relaxation region. As a result it is found that J(∞) does not vary linearly over the whole of the temperature range. The Barlow, Erginsav, and Lamb model of viscoelasticity fits the measurements well at high frequencies, but there is a small deviation at low frequencies.