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...

Full description

Saved in:
Bibliographic Details
Main Author: Yu, Xiang
Contributors: Parak, Wolfgang J. (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2014
Physik
Subjects:
Online Access:PDF Full Text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary: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.
DOI:https://doi.org/10.17192/z2014.0468