Post-graduate theses
Current Record: 4917 of 6548
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| Identifier |
000370060 |
| Title |
Development of functional Janus particles from hybrid colloidosomes |
| Alternative Title |
Σύνθεση λειτουργικών "Janus" σωματιδίων από υβριδικά κολλοειδοσώματα |
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Author
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Μοάτσου, Δάφνη Ιω.
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Thesis advisor
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Βαμβακάκη, Μαρία
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| Abstract |
Janus particles are named after the two-faced ancient Roman god, Janus, based on
the chemical and physical anisotropy that these particles exhibit. This work focuses
on the synthesis of sub-micron silica particles with asymmetric grafting of polymer
chains from their surface. High demand of such particles is in contrast to their usually
small-scale production. In response to that, this work takes advantage of the large
surface area provided by spherical latex particles to immobilize silica particles at the
latex-solvent interphase and thus provide shielding to one hemisphere of the colloidal
silica particles buried in the latex particles, whereas the exposed silica surface can be
chemically modified as required. Here, the exposed surface of the silica particles was
functionalized with atom transfer radical polymerization initiating sites. The
successful transformation of the particles into Janus precursor initiators was verified
by means of transmittance electron microscopy (TEM) and fluorescence microscopy.
These Janus initiator particles were used for the preparation of hybrid polymer-silica
Janus particles.
In order to successfully grow well-defined polymer chains from the surface of the
particles, the atom transfer radical polymerization conditions were optimized for each
monomer used. In each case, the polymerization kinetic studies provided information
on the reaction time and the control of the polymer molecular weight and molecular
weight distribution. The results show that high polymer molecular weight and narrow
molecular weight distributions are achieved, indicating the good control of the
polymerization reactions.
The Janus particles synthesized comprised an amine-functionalized hemisphere
and a polymer-grafted one. Three different polymers were grown from the particle
surface: a hydrophobic poly(methyl methacrylate) (PMMA) leading to amphiphilic
Janus particles, a hydrophobic poly(tert-butyl acrylate) (PtBuA) to give
polyampholyte particles that can be hydrolyzed to form an anionic and pH-responsive
derivative poly(acrylic acid) (PAA) and a hydrophilic cationic and pH- and
temperature-responsive polymer; poly(2-(dimethylamino)ethyl methacrylate)
(PDMAEMA), leading to fully hydrophilic cationic particles. For comparison, fullycoated
particles of the same polymers were also synthesized employing the same
polymerization conditions.
The successful grafting of the polymers from the surface of the silica particles was
verified by TGA while the high polymer molecular weight and narrow molecular
weight distributions were measured by GPC verifying the control of the surfaceinitiated
polymerization reactions. Based on the results derived from these techniques
the number of polymer chains grafted per particle was calculated, finding that for the
polymer-silica Janus particles this number was significantly lower than for the
corresponding fully polymer-coated particles. Observation by SEM provided insight
on the topology of the polymer-silica Janus particles, indicating the formation of
acorn-like and snowman-like particles.
The pH-depended size of the Janus PDMAEMA particles was shown by DLS
measurements verifying the pH-responsive behavior of the Janus particles. Although a
temperature-induced precipitation of the particles was observed by turbidimetry, the
size of the particles measured by DLS was not found to decrease before the LCST of
the polymer, as was the case for the fully-coated PDMAEMA particles. Instead, an
increase of the size of the particles was found attributed to the formation of controlled
aggregates.
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| Language |
English |
| Subject |
Polymer |
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Stimuli-response |
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Αποκρινόμενα πολυμερή |
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Ιανός |
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Πολυμερή |
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Σωματίδια |
| Issue date |
2011-11-16 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses
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Type of Work--Post-graduate theses
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| Permanent Link |
https://elocus.lib.uoc.gr//dlib/e/d/5/metadata-dlib-1321963086-404535-16972.tkl
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| Views |
208 |
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