Viscous, viscoelastic and dielectric properties of a perfluorinated polymer, Krytox 143-AB

Abstract

Measurements have been made of the viscoelastic and dielectric properties of a perfluorinated polymer, Du Pont Krytox 143-AB, of nominal molecular mass M_n= 4220, at atmospheric pressure within the temperature range –96 to +75°C. The viscosity and density have also been determined at pressures up to 312 MPa and temperatures from –41 to +62°C.

The high frequency viscoelastic retardational behaviour is described by the equation for the complex shear compliance J*(jω)=J_∞+ 1/jωη+FJ_∞/(jωηJ_∞)^β, with the parameters F and β changing from 5.1 and 0.52, respectively, below –30°C, to 4.0 and 0.60 above –15°C. An additional low frequency viscoelastic process is also found and is attributed to Rouse modes of polymer motion associated with a small proportion of high molecular weight material. The dielectric relaxational behaviour is described in terms of the complex permittivity by the Davidson–Cole equation ε*(jω)=ε_∞+(ε₀–ε_∞)/(1 + jωτ_D)^β_D, with the distribution parameter β_D increasing gradually from 0.56 below –30°C to 0.8 above 0°C.