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Oscillatory test: Frequency sweep


During the frequency sweep the frequency is varied while the amplitude of the deformation - or alternatively the amplitude of the shear stress - is kept constant. For the analysis the storage and loss modulus are plotted against the frequency. The data at low frequencies describe the behaviour of the samples at slow changes of stress. Oppositional the behaviour at fast load is expressed at high frequencies.

Frequency sweep

Frequency sweep:The graph shows a behaviour of G' and G'' that is typical for a polymer melt or polymer solution.


The frequency sweep is very important for polymer melts: By measuring frequency sweeps at different temperatures the characteristics like melting point, glass transition, rubbery-elastic characteristics, entanglement density, and processibility can be achieved. The measurement results can be superposed to significant master curves.

For dispersions (e.g. paints, cosmetics, comestible) the frequency sweep is less informative. Under favourable terms for this kind of samples this method can give a conclusion about their shelf life (sedimentation stability): If for low frequencies G' > G'', the dispersed particles should due to their gel structure still float and not sediment.


Rheology
 
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