Παρουσίαση PhD Λετζάκη Ελένης ΤΕΤΥ

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ΘΕΜΑ: Παρουσίαση PhD Λετζάκη Ελένης ΤΕΤΥ

ΑΠΟΣΤΟΛΕΑΣ: Charalampos Stratigis [mailto:stratigis@xxxxxxxxxxxxxxxx]

 

 

Πρόσκληση σε Δημόσια Παρουσίαση της Διδακτορικής Διατριβής της

κα. Λεντζάκη Ελένης

(Σύμφωνα με το άρθρο 12 του Ν. 2083/92)

Την Δευτέρα 28 Απριλίου 2014 και ώρα 11:00 στην αίθουσα Σεμιναρίων 3^ου ορόφου Τμήματος Φυσικής στο κτίριο του Φυσικού

θα γίνει η δημόσια παρουσίαση και υποστήριξη της Διδακτορικής Διατριβής της υποψηφίας διδάκτορος του Τμήματος Επιστήμης και Τεχνολογίας Υλικών κα. Λεντζάκη Ελένης με θέμα:

«Δυναμική και Ρεολογία Πρότυπων Διακλαδωμένων Πολυμερών»

 

«Dynamics and Rheology of Model Branched Polymers»

 

ABSTRACT

         The thesis focuses on the determination of the physical origin of chain stretch in complex branched polymers.  The uniaxial extensional rheology of linear polymers is rate dependent and the onset rate of experimental strain hardening (the macroscopic consequence of chain stretch) is equivalent to the theoretical prediction of the inverse Rouse time. The molecular dynamic picture becomes more complicated when introducing two or more branch points.  We study well-defined comb polymers (Roovers, 1979) with long molar mass of backbone M_b and rather short arms.  When systematically doubling the number of entanglements of the arms while keeping the M_b constant, the onset of chain stretch occurs at earlier rates. This can be rationalized by accounting for the effect of dynamic tube dilation and extra drag from the arms which results in an effectively slower stretch relaxation time. We modify the original differential pom-pom model by introducing drag strain coupling and by specifying the coupling of stretch between adjacent backbone segments.  The model is validated successfully by comparison with a wide variety of combs (with different molecular features) and a wide range of extensional rates. At high rates, the maximum stretch condition is reached and branch point withdrawal occurs, when arms are first oriented and then withdrawn into the stretched backbone tube segments, first from the free ends and then gradually progressing towards the centre.

Moreover, our study focuses on the effects of the environment on the reptation and fluctuations of model H and comb polymers. By systematically varying the length of the linear chains, we study the acceleration factor related to the arm and backbone relaxation times. The acceleration factor has a strong dependence on the length of the linear chains. We model the SAOS data using the Time Marching Algorithm by estimating a priori whether the linear polymer would be taken as a theta solvent or whether the reptation occurs in a skinny tube. The criterion for this estimation is based on the relaxation time scale separation between the linear matrix and the H or comb.

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Charalampos Stratigis

Secretariat

Dept. of Materials Science and Technology

University of Crete

P.O. Box 2208,

GR-710 03 HERAKLION, GREECE

Tel. +30 2810 394272

Fax. +30 2810 394273

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