Viscoelastic retardation of supercooled liquids

Abstract

A description is given of measurements made of the viscoelastic properties of six organic liquids in the supercooled state. A new experimental system has been used, which was designed to give results at 30 MHz of an order of magnitude greater accuracy than previous techniques. The measured values of the shear impedance were found to differ slightly from the predictions of the equation given by Barlow, Erginsav & Lamb (1967b), and the improvement in accuracy has made possible the determination of the retardational behaviour of liquids of viscosity,η, of about 1 P (0.1 Pas). The values of the retardational compliance,Jr, of the liquids investigated are found to lie within the range four to thirty times the limiting high-frequency complianceJ∞. The complex compliance functionJ*(jω) is described by the equationJ*(jω) =J∞+ 1/jωη +Jr/(1+jωτr)β. In this equation the last term, which describes the retardational behaviour, is similar to an expression used by Davidson & Cole (1951) in dielectric studies. In general the temperature dependence of the characteristic retardation time, τr, is found to differ from that of the Maxwell relaxation time ηJ∞. Extended studies of one liquid show the existence of two retardation processes. The results are discussed and shown to be consistent with the concepts of Davies & Matheson (1966) regarding the inhibition of molecular motions in viscous liquids.