Dynamic shear and compressional behavior of polydimethylsiloxanes: Ultrasonic and low frequency characterization |
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Authors: | C Verdier Pierre-Yves Longin Monique Piau |
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Institution: | (1) Laboratoire de Rhéologie Université Joseph Fourier 1, Institut National Polytechnique de Grenoble CNRS (UMR 5520) Domaine Universitaire BP 53 38041 Grenoble Cedex 9, France, FR |
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Abstract: | The dynamic rheological properties of a series of entangled polydimethylsiloxanes are investigated. Rheometrical shear measurements
are first reported for three different molecular weight samples, together with ultrasonic tests, thus allowing to obtain dynamic
shear master curves over ten decades. Winter‘s model for slightly polydisperse polymers is used and works well in this case.
This provides an example of the applicability of this model.
The propagation of longitudinal waves in the MHz range for the same PDMSs is studied next. The results are analyzed and combined
with static measurements of the compressibility. They indicate that different relaxation mechanisms have to be considered
in shear and compression, and that the ratio between volume and shear viscosity is frequency dependent, with a preponderance
for shear effects at higher frequencies. Shear and compressional relaxational mechanisms are also well separated. Moreover,
it is verified that the shear and compressional moduli are independent of the molecular weight in the transition region, above
a certain frequency. This frequency corresponds to a wavelength comparable to the distance between entanglements, in the case
of shear waves.
Received: 9 December 1997 Accepted: 30 March 1998 |
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Keywords: | Ultrasound rheometry shear polydimethylsiloxane compressibility dynamic moduli |
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