ISBN 9783843948272

978-3-8439-4827-2, Reihe Physikalische Chemie

Karin Koch
Ferronematic phases with strong coupling behavior based on liquid crystalline polymer decorated nanoparticles

228 Seiten, Dissertation Universität Köln (2021), Softcover, A5

Zusammenfassung / Abstract

The combination of magnetic nanoparticles and liquid crystalline (LC) phases leads to materials with unique magneto-optic behavior induced by a coupling between the magnetic director of the particles and the nematic director of the LC host. The strength of this coupling strongly depends on the stability of the particles against agglomeration, which is still the biggest challenge for the synthesis of stable ferronematic phases.

In this work, novel ferronematics are synthesized and fully characterized. Therefore, strategies for the compatibilization of nanoparticles with LC phases are developed in order to obtain stable ferronematic phases. For this purpose, nanoparticles are surface-functionalized with polymer brushes using a grafting-from process and a grafting-to process. For the grafting-from process, a novel route for the surface modification of nanoparticles with poly(dimethylsiloxane) (PDMS) brushes by surface-initiated ring-opening polymerization of cyclosiloxanes catalyzed by strong phosphazene bases and initiated by particle surface-attached hydroxyl groups is developed.

In the grafting-to process, side-chain liquid crystalline polysiloxane brushes are synthesized separately and then grafted covalently to the surface of nanoparticles of different magnetic behaviors. The functionalized particles are used as doping agents for the LC host 4-cyano-4’-pentylbiphenyl (5CB) in order to synthesize stable ferronematic phases. The impact of the different particles on the properties of the LC phase is systematically analyzed with respect to the dopant concentration. Furthermore, the magneto-optic behavior is investigated in magnetic field-dependent capacitance measurements.

In summary, the results of this thesis give important insights for the compatibilization of nanoparticles with LC phases and the production of stable ferronematics and contributes to a better understanding of the magneto-nematic coupling in the novel materials.