Current Topics for Research Internships or Bachelor Thesis | FB 09 - Physikalische Chemie

Synthese von Terpyridin-Derivaten zum Aufbau sequenz-kontrollierter Polymere
Assoziierende Polymere enthalten funktionelle Einheiten, die in der Lage sind durch nicht-kovalente Wechselwirkungen transiente Bindungen einzugehen und ein supramolekulares Polymernetzwerk zu bilden. Für systematische Studien an solchen Netzwerken eignen sich Vernetzungsmotive mit definierter Stöchiometrie und bekannter, variierbarer Bindungsstärke, wie beispielsweise die Bis-Terpyridin Komplexe verschiedener Übergangsmetalle. Um Struktur-Eigenschafts-Beziehungen solcher Gele systematisch untersuchen zu können, werden Terpyridin-funktionalisierte Polymere mit definierter Primärstruktur benötigt. Die in unserer Gruppe angewendeten Synthesestrategien zum Aufbau solch sequenz-kontrollierter Architekturen erfordern Terpyridin-funktionalisierte Aminosäuren und Diole.
Im Rahmen eines Forschungsmoduls oder einer Bachelorarbeit können etablierte Syntheserouten zur Herstellung von Terpyridine Aminosäure-Derivaten reproduziert, optimiert und anschließend in der Festphasensynthese eingesetzt werden. Alternativ ist auch die Mitarbeit bei der Synthese oligomerer Terpyridin-Diole möglich.

Betreuung: Katharina Breul (kabreul[a]uni-mainz.de)
Stand: Januar 2019; Starttermin: jederzeit

Dual-Dynamic Physical Networks
In the conventional polymer sciences, the mechanical properties of polymeric materials are engineered by manipulating different aspects of the chain architecture, such as the molar mass, branching, and chemical composition for thermoplastics, as well as the network microstructure in crosslinked gels. In contrast, in supramolecular polymers, the final properties are controlled through manipulation of non-covalent bonds, selected from a vast library with tunable association thermodynamics and kinetics. This approach is less demanding, since the bulk material can be tuned by varying small molecule components only, through the established molecule-to-material design concept. Recently, double network hydrogels have been developed based on the synergy of having two interpenetrating chemical networks, the first one highly crosslinked and the second one loosely crosslinked. At an optimal ratio of the two networks, the mechanical properties boost significantly, due to the sacrificial breakage of the chemical bonds in the first network. This hierarchy of structure is a well-known trick in nature to achieve multi-facet function. A similar approach has been widely used in the design of supramolecular double-network hydrogels, where a brittle first chemical network is replaced by different types of reversible supramolecular assemblies. In this project, which can be a research module or a Bachelor thesis, we aim to mimic the structure of double-network hydrogels by hierarchical design of a dually crosslinked physical hydrogel. For this purpose, tetra-PEG building blocks with different molar masses will be functionalized by ligands with significantly different association tendencies. A network with diverse and tunable dynamics can be obtained by simultaneous introduction of metal ions with different complexation affinity. We will then to study the structure and dynamics of the resulting materials using static/dynamic light scattering and rheology.

Supervisor: Mostafa Ahmadi (ahmadi[a]uni-mainz.de)
Time of posting: May 2019; possible start date: anytime

Stimuli-Responsive Supramolecular Hydrogels
Hydrogels are 3D network materials made of crosslinked hydrophilic polymer chains. Charged hydrogels have a high capacity for water uptake, up to 1000 times of their own weight; these materials are called superabsorbers and are commercially utilized in hygiene applications. Another class of hydrogels are supramolecular hydrogels in which hydrophilic polymer building blocks self-organize into a network by non-covalent bonds such as hydrogen bonding or ionic interactions. Due to the dynamic nature of these physical bonds, the sol–gel transition of supramolecular hydrogels can occur dependent on the environment such as temperature or pH. Therefore, different applications such as drug delivery, tissue engineering, and 3D printing can profit from them. This research project, which can be a Bachelor thesis or a research module, targets at combining the utility of both these types of hydrogels. Prototype samples will be fabricated by droplet-based microfluidics, and their water swelling capacity as well as their swelling/deswelling temperature range will be tuned by physical bonds and network architecture parameters. The project involves both preparative polymer-chemistry aspects, for example, preparation of hydrophilic polymer backbones with non-covalent cross-linking motifs as side groups, and analytical polymer-physics work, for example, assessment of the gel-sample mechanics by rheology.

Supervisor: Amir Jangizehi (amir.jangizehi[a]uni-mainz.de)
Time of posting: May 2019; possible start date: anytime

Design of Responsive Double-Dynamic Polymer Networks and Gels
Double-dynamic networks are the latest state-of-the-art in the field of soft elastomers. These networks combine two dynamic modes within the same material, and this offers a wide spectrum of different functionalities from stimuli responsiveness to self-healing. Double-dynamic networks can comprise one covalent and one reversible network, for example, in order to combine the advantages of both high mechanical strength and easy processability, or they can comprise one network with two different dynamic modes. The double-dynamic network we aim to design is of the latter type. In a Bachelor/Master Thesis or research module, you will be collaborating within a European project, with more information to be found here: https://www.dodynet.eu/. In particular you can be involved in one or more of the following aspects:

Synthesis of double-dynamic networks:
We have designed a novel double-dynamic network with a terpyridine dynamic bond and a thermo-responsive polymer that has to be optimized. The synthesis can include also the fluorescent labelling of the samples for probe diffusion techniques.

Characterization of double-dynamic networks with light scattering
Light scattering is a powerful technique that will help us to determine the homogeneity or defects in our polymer network. Moreover, it is useful to determine characteristic parameters of the polymer and the network such as the network mesh size.

Investigation of double dynamic-networks with probe diffusion techniques
Probe diffusion techniques include fluorescence correlation spectroscopy, fluorescence recovery after photobleaching, and dynamic light scattering. With a probe it is possible to investigate the permeability of the polymer network.

Supervisor: Paola Nicolella (p.nicolella[a]uni-mainz.de)
Time of posting: May 2019; possible startdate: anytime

Evaluieren & Etablieren neuer Messmethoden am Konfokalmikroskop
Gegenwärtig werden in unserem Arbeitskreis unterschiedliche Untersuchungsmethoden eingesetzt, um bei uns synthetisierte Polymergele zu charakterisieren. Dieses Spektrum soll am Konfokalmikroskop um zwei weitere Verfahren erweitert werden, mit denen thermische sowie mechanische Einflüsse untersucht werden können. Im Rahmen der Entwicklung neuer Messzellen sind dabei unterschiedliche chemische Tests notwendig, das heißt es muss zum einen ermittelt werden für welche Substanzen bzw. Messbereiche die neuen Verfahren anwendbar sind und zum anderen muss aus chemischer Sicht die Anforderungsliste an das neue Equipment näher spezifiziert werden. Hierbei soll in enger Abstimmung mit unserem Laboringenieur an der Entwicklung des Messsetups gearbeitet werden. Interesse an technischen Messverfahren sowie Spaß am Umgang mit Messgeräten sind dabei wünschenswert.

Betreuung: Holger Adam (hadam[a]uni-mainz.de)
Stand: Mai 2019; Starttermin: jederzeit