Viscoelastic properties of polymer melts and solutions under uniaxial extension
(2023)
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- Abstract
- Understanding the extensional behavior of polymers is necessary for several industrial applications, in which strain-hardening is often a criterion for guaranteeing the quality of the final product. While several models have been proposed to predict the extensional behavior of polymer melts, they usually cannot explain with a clear molecular picture why strain-hardening is much stronger in oligomeric solutions than in their monodisperse counterparts. To answer this question, we first focused on linear monodisperse samples and showed that a universal behavior on polymer chemistry could be retrieved in extension, which is strain-rate-thinning for sufficiently high strain rates. We then proposed a molecular picture based on the blob theory and Rouse relaxation modes to explain this behavior and quantified the magnitude of strain-rate-thinning, which is chemistry-dependent. To unravel the extensional behavior of oligomeric solutions and binary blends in general, we then examined the effect of constraint release mechanisms on polymer relaxation. In this work, we examined first self-unentangled samples to define the characteristic time of constraint-release events, which follows a universal expression on polymer chemistry, before investigating in details the relaxation mechanisms in a binary blend and evidencing the existence of an intermediate tube level, giving rise to the tension-equilibration process. Finally, we addressed the more complex case of binary blends in extension, focusing on the two extreme cases of well-entangled and oligomeric matrices. Thanks to the analysis of extensional viscosity data, we showed that an additional stretching mechanism gives rise to the stronger strain-hardening observed for these samples. Based on the blob theory and on the understanding of constraint-release mechanisms, we proposed a new molecular picture to explain the origin of this mechanism, consistent for both oligomeric solutions and binary blends of well-entangled linear chains.
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Hannecart, C. (2023). Viscoelastic properties of polymer melts and solutions under uniaxial extension. https://hdl.handle.net/2078.5/102266