Rheometer

Rheometer

Description

The linear viscoelasticity of polymer melts (and viscous fluids) is characterised in the time-temperature domain in shear, e.g. as shear modulus G(w), G(t), or viscosity h(w), using Rheometrics RDAII, RDSII or RMS800 rotational rheometers in a dynamic mode. The classic cone and plate or parallel disc geometries are used for polymer melts or fluids with an angular frequency range from 0.001 to 100 radians/second and a temperature range to more than 400C. Steady viscosity and normal stress difference are available in the steady shear mode. G(w) and G(t) for polymers in the solid phase are obtained from torsional oscillation of a rectangulat bar, typically from temperatures around -100C upward. Non-linear rheology, e.g. as the transient viscosity from a rate dependent stress- growth, or strain dependent relaxation modulus, G(g,t), is studied using the same rotational rheometers in shear. The ranges of strain and strain rate depend on geometry. Measurements have been made with less than 50mg. of research polymer. The equivalent transient extensional viscosity from stress-growth and strain dependent tensile relaxation modulus, E(e,t), are studied using a Rheometrics-Meissner elongational rheometer (RME). Approximately 1gm. of polymer is extended as a rectangular section strip to a maximum Hencky strain of 7 at strain rates from 0.001 to 1 /s. The temperature range extends to above 200C. All measurements in both shear and extension are in either a nitrogen or dry air environment.

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