Viscoelastic properties oscillatory shear rheometer

Because polymers have viscoelastic properties, rheometry is often employed to simultaneously measure both elastic and viscous parameters. To measure the viscoelastic properties using a rheometer, an oscillatory shear force/shear stress is applied to the material. Because of the viscoelasticity, the sample s deforma-tion/shear strain exhibits a phase lag to the shear force/shear stress. When the applied shear stress is ... 

Dynamic viscoelastic parameters such as the storage modulus and the loss modulus offer another measure of the mechanical properties of hydrogels. The storage and loss moduli represent the stored energy (elastic portion) and the heat dissipated (viscous portion) respectively of a viscoelastic solid. These are determined using a rheometer. The most commonly used set up for these measurements is the rotational rheometer wherein the sample is placed between two discs, the top disc rotates in an oscillatory manner in order to introduce a small strain oscillatory shear, while the torque exerted by the sample on the lower disc is measured. This allows a shear stress-strain relationship to be determined and thus for the moduli in turn to be found. Usually an amplitude sweep will be done to ensure that the sample is in the linear viscoelastic range [73, 75, 79, 80]. 

The rheological behavior of the copolymers was measured with a DynAlyser 100 stress-control rheometer (EUieoLogica) equi] d with a cone and plate at 25 C. The radius of the cone is 40 mm, and the angle between the cone and plate is 4.0°. Steady shear and oscillatory flow measurements were conducted to obtain the steady shear viscosity and dynamic viscoelastic properties of polymer solutions. 

The rheological behaviour of molten polymers is of prime importance as it relates to their microstructure and governs their processing characteristics [1]. Rotational rheometers, specifically cone-plate, parallel plate, and sliding plate rheometers are routinely used to characterize the linear viscoelastic properties of polymer melts. Small amplitude oscillatory shear experiments are employed to measure the storage (G ) and loss moduli (G"), which are related to the elastic and viscous character of the material, respectively, and the complex viscosity (77 ) as functions of angular frequency (a). 

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