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Identifier

000397555

Title

Ανάπτυξη υβριδικών νανο-κολλοειδών διασπορών τύπου πυρήνα-κέλυφους

Alternative Title

Formation of hybrid nano-colloidal dispersions with core-shell topology

Author

Κρασανάκης, Φανούριος Κ

Thesis advisor

Αναστασιάδης, Σπύρος

Reviewer

Βαμβακάκη, Μαρία
Βλασσόπουλος, Δημήτριος
Κουτσός, Βασίλειος
Μήλιος, Κωνσταντίνος
Παυλοπούλου, Ελένη
Ρίζος, Απόστολος

Abstract

The colloidal dispersions are heterogeneous systems of particles which are dispersed in a continuous medium. The combination between the nature of the particles and the medium leads to a huge number of different systems, defining their properties and their applications at the same time. The study of such systems helps the optimization of their properties and their further development to novel applications. The microgels are a very important category of colloidal dispersions where the dispersed phase consists of chemically crosslinked polymeric spheres. These spheres have the ability to respond to external stimuli by changing their size or other physicochemical properties of the polymer. This ability, in combination with the ability of capturing several types of ions or molecules, renders microgels suitable for applications in drug delivery, biotechnology, catalysis and colors industry, due to their improved rheological properties. The aim of the present thesis is the formation of pH responsive core – shell microgels. The ability of capturing small ionic molecules and metal ions for the formation of metal nanoparticles was also studied. Finally, novel microgel morphologies such as the chemically crosslinked polymeric capsules, where the core consists of solvent, were synthesized and examined. The monomers used for the synthesis of the polymeric spheres were the 2-(Diethylamino)ethyl methacrylate (DEA) and the tert-Butyl methacrylate (tBuMA) which is the protected form of the methacrylic acid (MAA). PDEA is a polymer base and PMAA is a polymer acid, resulting to the growth of microgels which respond to pH changes. First of all we synthesized homopolymer microgels by emulsion copolymerization of DEA and tBuMA with the crosslinker EGDMA while a microgel with a tBuMA core and a DEA shell was also prepared. Then the tBuMA was hydrolyzed in order to form MAA. The resulting colloidal particles were characterized by dynamic light scattering which allowed the determination of the pH influence at the hydrodynamic radius of the particles, scanning electron microscopy that gave information on the morphology and the size homogeneity of the particles and potentiometric titrations for the study of the microgel’s ionic behavior and the determination of the dissociation constant, pKα. After the characterization of the synthesized microgels, the capability of capturing small ionic molecules through electrostatic interactions was studied. More specifically, we examined the electrostatic interactions between a dye with negative charge (4-(2-hydroxy-1-naphthylazo)benzenesulfonic acid sodium salt, Acid Orange 7) and the PDEA which is positively charged at low pH due to its amine protonation. UV – Vis spectroscopy was employed for the determination of the dye percentage that was captured by the polymeric particle. Upon discharging PDEA by increasing the pH, we estimated the fraction of dye that was released to the solution and the fraction that remained inside the microgels. Thus we studied the influence of the microgel’s architecture on the captured and released percentage of the dye. The influence of the dye’s excess and the dye’s charge to the uptake procedure was also studied. We also prepared metal nanoparticles inside the synthesized microgels. More specifically, we studied the growth of platinum nanoparticles within the PDEA microgels and of iron oxide nanoparticles (magnetite) within the PMAA microgels. The hybrid materials were characterized by dynamic light scattering, transmission electron microscopy and X-ray diffraction in order to confirm the presence of the nanocrystals and to determine their size. For further information about the size and the topology of the nanocrystals, the hybrids were also characterized by small angle X-ray scattering. In the last part of the present thesis we synthesized hollow capsule microgels. For the formation of the capsules three different synthetic techniques were used. During the two first techniques core – shell particles were synthesized with a degradable hydrophilic and a degradable hydrophobic crosslinker at the core, respectively. After the degradation of the crosslinker at low pH by breaking the crosslinks, the free chains were removed through diffusion. During the third technique core – shell microgels were synthesized with non-crosslinked polymer chains at the core. These chains were then removed from the particle through diffusion in a good solvent. After cleaning the colloidal dispersions from free chains, the polymeric capsules in all three cases were characterized by dynamic light scattering in order to examine the influence of the core absence to the hydrodynamic radius. We also performed scanning electron microscopy measurements to confirm the hollow structure of the particles and potentiometric titrations to define their ionic behavior. The different routes followed for the formation of polymeric capsules were compared to each other in order to study the influence they have to the final capsule, since each technique can be used for a different application. Finally we studied the influence of the shell thickness to the swelling properties of the capsules.

Language

Greek

Subject

Capture and release

Colloidal dispersions

Degree of swelling

Hollow capsules

Hydrophilic and hydrophobic

Ionic behavior

Metal nanocrystals

Microgels

Poly(methacrylic acid)