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Identifier |
000399641 |
Title |
Linear and non-linear rheology of heterogeneous polymeric systems : from entangled polymeric networks and elastomers to nanocomposites |
Author
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Dessi, Claudia
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Thesis advisor
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Βλασσόπουλος, Δημήτριος
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Reviewer
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Benoit, Loppinet
Φυτάς, Γεώργιος
Πετεκίδης, Γεώργιος
Moshe, Gottlieb
Frank, Snijkers
Βαμβακάκη, Μαρία
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Abstract |
Since more than one hundred years ago the discovery of polymerization mechanisms that
allowed obtaining polymeric systems with precise and complex molecular structures has
fascinated scientists from all over the world and dramatically changed the concept of industry
production and our daily life. The reason why industrial polymers have got such great attention
in many different scientific and technological applications is the existence of an intimate
relationship between their molecular structure and rheological properties with final processing
and mechanical properties. As a result, industrial standard methods were intensively
developed which most of them allow to obtain easily and quickly important structural and
mechanical information for the final application to which the material is intended. However,
some technical issues may not be properly taken into account given a wrong characterization
of the material. One of the most common industrial dynamic mechanical test employed in
order to characterize the rheological response involve torsion deformations. Torsion
measurements are in general performed on stiff and elastic materials, such as non-filled and
filled vulcanized rubbers, in order to overcome instrument compliance issues and/or wall slip
phenomena between the sample and the testing geometry that may importantly affect the
measurement itself. In the first part of this work we clearly show that large departures of the
rubbery modulus for industrial elastomers may occur when dynamic mechanical
measurements are performed in torsion according to industrial standards. The testing sample
was chosen in such a way that a comparison with the most common and reliable rheological
protocol, small amplitude oscillatory shear, was possible. Once compliance issue and other
possible sources of errors were addressed, experimental results in dynamic torsion
measurements were found to depend on specimen geometry and its aspect ratios, and the
sample loading by clamping. However, so far the empirical corrections proposed do not
completely fulfilled the experimental artefact. This observation made this work necessary to
establish a better guideline that allows more reliable torsion dynamic mechanical
measurements in industrial standard protocols.
One of the class of polymer materials that obtain extensive application in the
technology field (in particular rubber technology) is represented by the category of filled
polymers. It is well-known that the addition of fillers into a polymer matrix generates
mechanical reinforcement in the resulting polymer compound. However, the reinforcement
mechanism still remains in debate since it does strongly depend on the specific chemistry and
properties resulting from polymer-particle interactions. More specifically, the role of the
presence of a bound polymer layer on particle surface is not completely addressed. One
strategy in order to investigate the reinforcement mechanism is to study the rheological
response of favorably interacting filled polymer systems. The second part of this work, hence,
is focused on a better understanding of the polymer-particle flow dynamics in nanofilled
model polymers for which the presence of bound polymer layers was not always possible to
assess. Surprisingly, rheological results show a clear transition from polymer dominated
dynamics into “glassy” network dynamics leading to a percolated behavior. These findings
encouraged us to further investigate the nature of the polymer-particle interactions in the
percolated structure that was found to be most likely related to the presence of hydrogen
bonds.
Another peculiar feature of the mechanical behavior shown from polymer systems is
the capability to be deformed to large amplitude deformations without losing their
macroscopical shape. Often large deformations are oscillatory and industrial rubbers widely
fulfill this characteristic. Despite mechanical properties in large deformations of polymer
network have been observed and investigated for more than six decades, addressing a proper
physical model description to the material response remains a challenge. The last part of this
work took up the chance to develop a new continuum model that for the first time can describe,
at least qualitatively and partially quantitatively, the experimental asymmetric hysteresis
response of filled industrial rubbers when they are subjected to large amplitude oscillatory
deformations in uniaxial extension superimposed to a steady one.
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Language |
English |
Subject |
Network systems |
Issue date |
2016-02-05 |
Collection
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School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Doctoral theses
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Type of Work--Doctoral theses
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Permanent Link |
https://elocus.lib.uoc.gr//dlib/a/7/4/metadata-dlib-1456306201-821140-18615.tkl
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Views |
517 |