title: Supramolecular Systems Based On Trisamides With Linear Perfluorinated Side Chains
Creators: name: Czich, Steffen
Publisher: name: University of Bayreuth
Year: 2021
Subjects: subject: Trisamides
subject: Perfluorinated Side Chains
subject: Mesophase
subject: Liquid Crystalline
subject: Self-Assembly
subject: Melt Electrospinning
subject: 500
subject: 540

description: Supramolecular chemistry is the chemistry of molecular assemblies and intermolecular bonds. In contrary to the traditional chemistry, which deals with covalent chemical bonds, supramolecular chemistry is a matter of physical interactions between molecules. These non-covalent interactions determine the spatial organization of molecules, which can lead to the formation of larger well-defined supramolecular objects. In the supramolecular approach, molecules are able to self-assemble reversibly to defined supramolecular objects. The shape and functionality of these objects are imbedded in the molecular structure of the single molecules, which are influenced by the geometry of the molecule, side chains, and functional groups. In this context, this thesis provides a systematic study and detailed characterization of the thermal properties, phase behaviors, and mesophase structures of 1,3,5-benzenetrisamides (BTAs) and one 1,3,5-cyclohexanetrisamide (CTA) with linear perfluorinated side chains of different lengths. BTAs based on 1,3,5-triaminobenzene pass through plastic crystalline or liquid crystalline mesophases, which can mostly be identified as columnar phases. BTAs based on trimesic acid have one or more mesophases between the solid state and the isotropic phase, which are mostly of liquid crystalline appearance but cannot be clearly identified as columnar phases. All BTAs show an increase in transition enthalpy at the melting temperature and a simultaneous decrease at the clearing temperature with increasing side chain length. Comparison between the BTAs based on the different cores shows, that the BTAs based on 1,3,5-triaminobezene have lower clearing temperatures and much lower melting temperatures than the BTAs based on trimesic acid. The column distances of all perfluorinated BTAs increase linearly by a value of about 0.1 nm for every additional CF2 unit in the side chains. The CTA passes through an unidentified liquid crystalline mesophase and a columnar nematic phase before it finally changes into the isotropic phase upon heating. A selection of two BTAs based on 1,3,5-triaminobenzene with different side chain length and the CTA were processed by melt electrospinning to thin supramolecular fibers. The electrospinning parameters were varied to find the best parameter set for supramolecular fibers with good fiber shape and quality. The BTAs form the best fibers processed from the isotropic phase and at applied electric fields of 5.0 kV/cm and 6.7 kV/cm with average fiber diameters of about 0.4 µm up to 0.5 µm. The CTA forms thin fibers from the nematic phase with average fiber diameter of about 1.7 µm. Furthermore, the conditions for the processing of comparably thick fibers in the range of 5 µm up to 15 µm for direct force measurements of various BTA and CTA compounds within a collaboration with the chair of Physical Chemistry II at the University of Bayreuth should be found. All compounds could be processed to fibers of the desired thickness in an electric field with a strength in the range of 2.5 kV/cm up to 5.0 kV/cm. Two of them were already used for direct force measurements. Wettability measurements with a polar and a nonpolar liquid of fiber mats of BTAs with perfluorinated and alkyl hexyl side chains resulted in an about 20 degrees higher contact angle for the fluorinated BTA type with the polar liquid, and an about 70 degrees higher contact angle with the nonpolar liquid. Selected BTAs with different cores and perfluorinated side chain lengths were chosen for self-assembly investigations of a single BTA from a single solvent. In a second approach, the co-self-assembly of two structurally related BTAs from the same solvent mixture was investigated. All BTAs form thin fiber bundles with uniform surface only from a few solvents with concentrations of 0.1 wt.% and below. The best results were obtained from ortho-dichlorobenzene. Fiber bundles with average fiber diameters of about two micrometers for the BTAs based on 1,3,5-triaminobenzene with side chains of three and five carbon atoms, as well as fiber bundles with average fiber diameters in the range of only 0.1 µm up to 0.2 µm formed by the BTA with side chains of seven carbon atoms were obtained. BTAs based on trimesic acid form fiber bundles from only a few solvents at a concentration of 0.1 wt.% but it is not possible to obtain fiber bundles for all three BTAs with different side chain lengths from the same solvent, which is necessary for a proper comparison. Two BTAs, one bearing perfluorinated and one alkyl side chains, were chosen for the co-self-assembly study. The experiments were performed in polyamide wovens as support scaffolds and from a solvent mixture of methyl ethyl ketone and ortho-dichlorobenzene. The co-self-assembly resulted in formation of two different morphologies, which indicate that a separate columnar self-assembly process takes place where each of the compounds forms single fibers.