Authors:	Koziol, Martha Franziska
Title:	Interplay of Structure and Dynamics in Metallo–Supramolecular Polymer Networks
Online publication date:	25-Jul-2022
Year of first publication:	2022
Language:	english
Abstract:	The present thesis focuses on the interplay of structure, mechanical response, and dynamics in model-type supramolecular polymer networks. Reversible networks formed by star-shaped monodisperse macromolecules that are interlinked via metal-ligand interactions (dative transition metal-terpyridine bonds), serve as material basis to establish structure-property-relationships. To fully unravel the dynamics in such transient networks, contributions from all network-forming components (e. g. polymer chain physics or chemistry of sticky motifs) and their mutual dependences have to be considered. The first part of this thesis addresses the characterization of poly(ethylene glycol) (PEG) solutions in the semi-dilute concentration regime. A low-frequency plateau in the storage modulus as indicated by rheology, leads to the assumption of a weak energy-storing substructure. However, static and dynamic light scattering results demonstrate no aggregate or cluster formation in the polymer solutions if special care is taken during sample purification and preparation. The frequency range accessible by rheology experiments is extended to higher frequencies by several decades using coated spherical gold nanoparticles as microprobes. The results underline the urgent necessity of a thorough sample purification by means of filtration if artefact-free light scattering autocorrelation functions are targeted. In a second study, the scattering behavior of transiently connected supramolecular polymer networks is investigated. The combination of static and dynamic light scattering simultaneously provides information about the network structure (static inhomogeneities), as well as the underlying relaxation processes and their length scale-dependence. A delayed gel preparation procedure is implemented that allows for externally tunable gelation times and a facilitated preparation of the mandatory dust-free gels for light scattering experiments. This new method opens up the opportunity to monitor the scattering intensity and evolving of relaxation modes in real-time during gelation, and enables the postulation of a molecular gelation mechanism. A targeted control of network relaxation times is achieved through the use of either cadmium, zinc, or nickel cations as their metal-terpyridine dissociation constants differ by several orders of magnitude. The combination of multiple characterization techniques (rheology, DLS, SLS, FRS, UV-Vis) is required to scan a length scale and timescale range of five, respective 15 decades, and to gain knowledge on the complex hierarchy of relaxation processes in the networks. The macroscopic terminal relaxation times measured by rheology and the relaxation modes obtained by dynamic light scattering are examined, as well as the self-diffusivities of fluorescently labelled four-arm macromolecules measured by forced Rayleigh scattering. These kinetically controlled relaxation times are related to the complex dissociation of an isolated zinc-terpyridine bond and the resulting activation energies are compared. Static inhomogeneities in the range of several tens of nanometers are detected by static light scattering thereby unravelling a direct impact of the local structure on the viscoelastic intensity autocorrelation modes. A further approach towards desired structure control in transient networks is presented in the last part of this thesis. The above introduced star-PEG network structures are modified by systematically incorporating connectivity defects to independently investigate the influence of connectivity mismatches on the mechanical properties and self-diffusivities. Despite a constant overall sticker concentration, an increasing defect fraction leads to a decrease in the elastic response. In addition to that, the microscopic structural irregularities further impact the center-of-mass diffusion of entire macromolecules within the network. The increased number of intramolecular loops coming along with an apparent dilution effect, leads to an accelerated diffusion. These fundamental relations have an enormous importance especially in the field of smart material design of self-healing materials with intrinsic transport properties.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-7294
URN:	urn:nbn:de:hebis:77-openscience-9360ca26-62c5-4603-816a-88d73e1ff1886
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	http://rightsstatements.org/vocab/InC/1.0/
Extent:	VIII, 155 Seiten, Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen