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| Identifier |
000351446 |
| Title |
Διάδοση ελαστικών /ακουστικών διεγέρσεων σε δομικές αλλαγές σε δοκίμια πολυπροπυλενίου |
| Alternative Title |
Propagation of acoustic/elastic excitations of polypropylene industrial samples |
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Author
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Βουδούρης, Παναγιώτης Ευάγγελος
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Thesis advisor
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Φυτάς, Γεώργιος
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| Abstract |
The aim of this thesis was the experimental investigation of the elastic properties of thin films of nanocomposite materials which consist of polymer reinforced with
inorganic nano-sized particles. For the determination of the main properties of the individual components, the behavior of model polymers as well as nanoparticles was studied.
For amorphous polymer systems of polypropylene (PP) and polyisoprene (PI), we employed Brillouin light scattering (BLS) at temperatures far above the glass transition
temperature (Tg+100K) where we obtained the characteristic relaxation time of the longitudinal modulus M*. We found that the characteristic relaxation time, irrespectively of the fitting procedure, is faster than the α-relaxation which obeys the non-Arrhenius VFT equation. Albeit, this has been noticed, it remains a puzzling finding in glass forming systems. The available knowledge is based only on temperature dependent BLS experiments performed, however, at a single wave vector (frequency). Using a new BLS spectrometer, we studied the phonon dispersion at GHz frequencies in molecular (oterphenyl,
OTP) and polymeric (polyisoprene, PI and polypropylene, PP) glass formers.
We found that the hypersonic dispersion does relate to the glass transition dynamics but the disparity between the BLS-relaxation time and tα is system dependent. In PI and PP, the former is more than one order of magnitude faster than tα, whereas the two relaxation times become comparable in the case of OTP. The difference between the two relaxation times appears to relate to the “breath” of the relaxation time distribution function. In OTP the α-relaxation process assumes a virtually single exponential decay at high temperatures well above the glass transition, in clear contrast to the case of the amorphous bulk polymers.
In order to add one more technique for the investigation of α-relaxation at
temperatures far above Tg we employed fluorescence correlation spectroscopy experiments on amorphous polymer samples and we found that under specific conditions
τα can be subtracted from the diffusion coefficient of a fluorescent molecule diffusing in polymer sample investigated.
Concerning the nanoparticles, we used two core (SiO2) – shell (polystyrene) particles with different grafting densities (600- 1100 chains/core). For these particles we determined their shape and size in dilute suspensions using photon correlation spectroscopy. In concentrated samples where the particles are close to each other, we
found that after a critical concentration the interpenetration of the polymeric shell is possible. For the particle where the grafting chains are long and few, the interpenetration appears at concentration close to the overlap concentration. For the particle where the
grafting chains were more and shorter the interpenetration of the grafting chains appears at concentration much bigger than the overlap concentration.
The particles above were dispersed in polystyrene matrix and supported thin films samples were prepared with the concentration of SiO2 varying form 1.2-30%wt. We employed Brillouin light scattering experiments at two different scattering geometries from where we obtained the elastic properties parallel and normal to the film surface. We found that the elastic properties of the polymer-coated particle thin films are different form the polymer matrix. Furthermore the results showed an unexpected mechanical anisotropy, the out-of-elastic properties in the particle films and particulate PS falls lower
than the value in the neat PS. In contrast, the in-plane elastic properties increase in the particulate PS films above the bare PS value.
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| Language |
Greek |
| Subject |
Brillouin Light Scattering |
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Core Shell Particles |
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Elastic Properties of Thin films |
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Fluorescent Correlation Spectroscopy |
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Glass Transition Dynamics |
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Phonons |
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Photon Correlation Spectroscopy |
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Polymers |
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Δυναμική Υαλώδους Μετάβασης |
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Ελαστικές ιδιότητες Λεπτών Υμενίων |
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Πολυμερή |
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Σωματίδια Πυρήνα Μανδύα |
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Φασματοσκοπία Συσχέτισης Φωτονίων |
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Φωνόνια |
| Issue date |
2009-06-30 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Doctoral theses
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Type of Work--Doctoral theses
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| Views |
273 |
Διάδοση ελαστικών /ακουστικών διεγέρσεων σε δομικές αλλαγές σε δοκίμια πολυπροπυλενίου
