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And Author="Loppinet"
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| Identifier |
000399645 |
| Title |
Metastability transitions in colloidal supramolecular systems of varying softness and shape |
| Alternative Title |
Μετασταθείς μεταπτώσεις σε κολλοειδή υπερμοριακά συστήματα με μεταβλητή χαλαρότητα και σχήμα |
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Author
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Μαράκης, Ιωάννης
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Thesis advisor
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Βλασσόπουλος, Δημήτριος
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Reviewer
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Πετεκίδης, Γεώργιος
Φυτάς, Γεώργιος
Domenico, Truzzollilo
Pavlic, Lettinga
Benoit, Loppinet
Φλούδας, Γεώργιος
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| Abstract |
In this research we explored the effects of softness on the metastability transitions
and in particular during gel or glass formation. More specifically, we studied the effects
of varying the molecular characteristics of a star polymer on the structural rearrangements
of the solution upon the appliance of an external flow field. We defined a 'softness
parameter', (SP), and highlighted its effect on the structural order of the system. We
investigated the effect of shearing parameters on the nucleation process and explained the
variations with the modifications of the particle rearrangements. The stability of the
structures was associated with softness and concentration, denoting the sensitive
dynamics deviations upon changing the molecular characteristics. Flexible shapes of
particles allow the systems to reform and accommodate better the external stimuli. We
pinpointed the differences of our soft systems with the hard spheres and highlighted the
complexity yielded by 'softness'. In general, softness and metastability are two terms,
which seem to be inextricably bonded, generating amazing properties.
We also, investigated the properties of two different self-assembled block copolymers.
The amphiphilicity of the molecules drive the systems to self-organize and form
hydrogels. Depending on the molecular characteristics, the hydrogel structures exhibit
varying properties showing solid structures in high concentrations. The elasticity of the
networks increase rapidly with concentration demonstrating different types of interactions
between the self-assembled structures. The hydrogels studied in this work, showed fast
reformation after the cessation of large shear rates, depicting strong interactions among
the large self assembled structures. By careful tuning hydrophobic and hydrophilic
interactions we can control the kinetic properties of such systems and mimic the natural
way of creating supramolecular systems.
4
Furthermore, we investigated the rheology of two hydrogels which were especially
synthesized for targeted drug delivery in pancreatic cancer tissues. The rheological
behavior of the hydrogels is highly dependent on pH and temperature since the gel flows
upon decreasing pH or increasing temperature. The thixotropy of the gel was studied by
applying high shear rates and then capturing the time needed for the gel to reform. Both
hydrogels manifested weak thixotropic behavior by instant reformation after the shear
cessation. The sensitivity in temperature and pH variations, makes these hydrogels
excellent candidate systems for drug delivery applications, offering discovery
opportunities in this important field.
Finally, we examined metastability effects in more complicated systems consisted of
two different sizes and types of particles. The initial soft colloidal system was perturbed
by adding depletion and displayed several phase transitions. The kinetic properties along
with mixture's elasticity, change as a function of depletion revealing a way to control the
behavior of such systems. Again, metastability was associated with softness and proved to
affect the mechanical properties of the mixtures. All, the experimental results were
supported by theoretical analysis and simulations, denoting the validity of our outcomes.
Also, simulations were performed for different size ratios and functionalities. The
combined results demonstrate that by tuning the physical parameters, like star
functionality and size ratio, we can steer the rheology of the mixtures.
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| Language |
English |
| Subject |
Phase transitions |
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Soft star polymers |
| 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/d/f/b/metadata-dlib-1456471096-449957-22675.tkl
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| Views |
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