Synthesis and characterization of particles fabricated by layer-by-layer assembly
The subject of this doctoral dissertation is the synthesis and characterization of microcapsules and nanoparticles fabricated by Layer-by-Layer (LbL) assembly. The technique is based on the electrostatically-driven alternated adsorption of cationic and anionic charged polymers in a layer-by-layer...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2014
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| Zusammenfassung: | The subject of this doctoral dissertation is the synthesis and characterization of
microcapsules and nanoparticles fabricated by Layer-by-Layer (LbL) assembly. The
technique is based on the electrostatically-driven alternated adsorption of cationic
and anionic charged polymers in a layer-by-layer fashion, similar to the layer
structure of an onion. During these syntheses polyelectrolyte multilayer shells were
formed via electrostatic interactions on calcium carbonate (CaCO3) microparticles
and gold (Au) nanoparticles (NPs). Due to differences in the size range between
microcapsules and nanoparticles, two different strategies were used for the
self-assembly of polyelectrolytes.
This work first aimed to investigate the LbL assembly of polyelectrolytes
oppositely charged on calcium carbonate spherical particles, which size diameter
ranges from 1 to 6 μm. Polyelectrolytes with different nature property have been
employed to produce polyelectrolyte multilayer (PEM) capsules: i) sulfate/polyarginine
(DEXS/PARG) for biodegradable shell formation and ii) poly(sodium-
4-styrenesulfonate)/poly(allylamine hydrochloride) (PSS/PAH) for non-biodegradable
shell formation. In addition, one kind of silica (SiO2) capsules have been
fabricated and their properties such as degradability and release of molecules have
been compared with polyelectrolyte capsules. In order to encapsulate different
molecular cargo inside the capsules (with silica or polyelectrolyte shells), two main
procedures have been employed: i) co-precipitation (or pre-loading) and ii)
post-loading. The encapsulation efficiency of both procedures has been
investigated.
Moreover, multifunctional capsules have been produced by embedding magnetic
NPs or plasmonic NPs into the hull of the capsule. The functionalization was
performed using again electrostatic interactions as the major driving force in the
assembly between nanoparticles and polyelectrolytes. Thus, some applications of
these carrier systems for delivery and sensing were investigated. Firstly,
polyelectrolyte capsules post-loaded with the pH indicator seminaphtharhodafluor
(SNARF) in their cavity with and without polymer coated iron oxide NPs in their
hull were synthesized. The composition of the walls of these magnetic PEM
capsules was (PSS/PAH)2 magnetic NPs (PSS/PAH)2. The results indicated that
encapsulated ion-sensitive fluorophores can be used to detect fast changes of pH
and the capsules can be manipulated (i.e., change the location) in microfluidic
devices using magnetic fields. Finally, non-biodegradable capsules loaded with
cubic magnetic NPs were produced to study their opening upon the application of
an alternating magnetic field. The polymer poly(acrylamide-co-diallyldimethyl-
ammonium chloride) (P(Am-DDA)) which is strongly positively charged
was added within the polyelectrolyte shell to enhance the attachment and increase
VI
the concentration of magnetic NPs. The final architecture of the LbL shell was
(PSS/PAH)(PSS/P(Am-DDA) magnetic NPs (PAH)(PSS/PAH)2. Magnetic NPs can
be heated by the application of an alternating magnetic field. This fact was used to
disrupt and open PEM capsules containing magnetic nanoparticles in the shell. The
capsules released then their molecular cargo loaded in their interior. |
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| DOI: | 10.17192/z2014.0468 |