Towards magneto-elastomeric nanocomposites with supramolecular activity

Fruhner, Lisa Sarah; Förster, Stephan Friedrich (Thesis advisor); Richtering, Walter (Thesis advisor)

Jülich : Forschungszentrum Jülich GmbH, Zentralbibliothek, Verlag (2021)
Book, Dissertation / PhD Thesis

In: Schriften des Forschungszentrums Jülich. Reihe Schlüsseltechnologien = Key technologies 234
Page(s)/Article-Nr.: 1 Online-Ressource (XVI, 213 Seiten) : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

Combining the functionality of nanoparticles and polymers leads to a novel class of materials: nanocomposites. Nanoparticles like magnetic nanoparticles or quantum dots (QDs) can be used to introduce new properties into polymeric matrices. This could be the response to a magnetic field or photoluminescence. Polymers can provide stability, add elasticity or an improved processability, they can be functionalised by supramolecular groups to allow non-permanent bonds between the polymer chains. The combination of those properties makes nanocomposites deeply interesting for a range of applications like coatings, membranes, organic solar cells or biomedicine. The additional structuring of nanoparticles within the polymer matrix allows for an even wider range of tuneable properties.Obtaining stable nanocomposites in external fields is highly desirable but challenging due to the usually encountered aggregation of nanoparticles in polymer matrices. Therefore, compatibilization of the two components is essential to study their controlled spatial organisation. The aim of this work is the development of a route towards magneto-elastomeric nanocomposites with supramolecular activity. For this, functional nanocomposites are synthesised, and their structure characterised by small-angle scattering methods. First, the behaviour of superparamagnetic, oleic acid stabilised iron oxide nanoparticles, in a magnetic field is investigated by small-angle neutron scattering (SANS). It is found that already at low magnetic fields, the nanoparticles form chains, which are aligned parallel to the magnetic field while crystalline phases dominate the measured structures at higher field strengths. To be able to make use of this behaviour in a nanocomposite, a compatibilization of the nanoparticles and the polymer matrix is necessary. The solution developed here, relies on the coating of the nanoparticles with a polymer shell. This is achieved in the second part of this thesis by encapsulating the nanoparticles with a polydiene-poly(ethylene oxide) (PEO) diblock copolymer. In this process the polydiene forms a cross-linkable inner shell to chemically fixate the polymer around the nanoparticle. The PEO corona allows the dispersion of the nanoparticles in water or PEO melt. Small-angle X-ray scattering (SAXS) is used to investigate the encapsulation procedure, showing that the critical step is the phase transfer from organic medium to water, and the final nanocomposites, revealing well-dispersed nanoparticles in the polymer melt. The same encapsulation procedure is used to create clusters of QDs whose distances can be tuned by different polymer sizes. The polymer shell enabled long-term stability of these materials and high-power excitations. Finally, shifting the focus towards elastic and supramolecular materials, a polymer shell with hydrogen bonding groups is targeted. As the encapsulation procedure explained above only works for PEO based materials, another method has to be developed, in which poly(butylene oxide) PBO was chosen as the nanoparticle coating. The synthesis of these polymers involved the polymerisation of butylene oxide onto an initiator carrying a protective group and the subsequent independent functionalisation of both ends of the polymer chain with anchor group, binding to the nanoparticle surface, and hetero-associating supramolecular groups diaminotriazine (DAT) and thymine. First results showed that coating the nanoparticles with these polymeric ligands results in supramolecular interactions between DAT and thymine functionalised nanoparticles as revealed by SAXS studies and microscopy.

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