| Summary: | An electromagnetic transducer has been developed to measure the complex dynamic shear modulus of viscoelastic liquids as a function of frequency in the range 20c/s - 1.5Kc/s The test liquid is subjected to an oscillatory shear strain in an annular gap, and the variation of loading on the moving boundary as a function of the height of liquid in the annulus is reflected as a change in transfer Impedance at the transducer terminals. This change in electrical impedance may then be used to calculate the shear properties of the test liquid. The liquids investigated were four polydimethyl siloxane fluids of differing molecular weight. Measurements previously made on these fluids at higher frequencies have been extrapolated to low frequencies on the basis of a modified theory of Rouse and it is shown that these extrapolations coincide well with the low frequent experimental determinationse A theory has also been developed to attempt a correlation between the non-Newtonian behaviour of viscoelastic liquids under the influence of steady shear flow with the dynamic shear moduli. It appears that there is a functional relationship connecting the shear and normal stresses as a function of shear rate with the real and imaginary parts of the complex shear modulus as a function of angular frequency. In addition, the recoverable elastic shear strain in steady flow appears in the resulting equations and shows that the properties in oscillatory shear do not completely specify the behaviour in steady shear flow. Some comparison of the theory with experiment is given. Finally, some attention has been given to means of automatically calculating relaxation spectra from dynamic modulus data. Although various methods of performing this calculation have already been described, they usually involve laborious hand computation and are not amenable to direct programming for use on a computer. Two new methods are described one of which need involve only a simple hand calculation after a certain matrix has been pre-calculated This matrix does not depend on the data values and so needs only to be calculated once.
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