03 Fakultät Chemie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/4
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Item Open Access Counterion effects on the mesomorphic and electrochemical properties of guanidinium salts(2024) Ebert, Max; Lange, Alyna; Müller, Michael; Wuckert, Eugen; Gießelmann, Frank; Klamroth, Tillmann; Zens, Anna; Taubert, Andreas; Laschat, SabineIonic liquid crystals (ILCs) combine the ion mobility of ionic liquids with the order and self-assembly of thermotropic mesophases. To understand the role of the anion in ILCs, wedge-shaped arylguanidinium salts with tetradecyloxy side chains were chosen as benchmark systems and their liquid crystalline self-assembly in the bulk phase as well as their electrochemical behavior in solution were studied depending on the anion. Differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS) experiments revealed that for spherical anions, the phase width of the hexagonal columnar mesophase increased with the anion size, while for non-spherical anions, the trends were less clear cut. Depending on the anion, the ILCs showed different stability towards electrochemical oxidation and reduction with the most stable being the PF6 based compound. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest a possible contribution of the guanidinium cation to the oxidation processes.Item Open Access Methacrylate‐based polymer foams with controllable pore sizes and controllable polydispersities via foamed emulsion templating(2020) Dabrowski, Miriam Lucia; Stubenrauch, CosimaThis study reports on a novel templating route, which uses foamed emulsions as templates for porous polymers. The concept is based on the generation of a monomer‐in‐water emulsion, which is subsequently foamed via microfluidics. The monomer of choice is 1,4‐butanediol dimethacrylate (1,4‐BDDMA). After polymerization of the foamed emulsion, one obtains open‐cell polymer foams with porous pore walls. Foamed emulsions and polymer foams are generated. It is shown that foamed emulsion templating in combination with microfluidics is well‐suited to synthesize 1) monodisperse poly(1,4‐BBDMA) foams with controllable pore sizes and 2) their polydisperse counterparts with controllable polydispersities. Monodisperse templates with different bubble sizes and thus polymer foams with different pore sizes ranging from about 100-400 μm in diameter are synthesized. Microfluidics is also used for the generation of polydisperse poly(1,4‐BDDMA) foams with polydispersities between 18% and 27% but the same mean pore sizes as the monodisperse ones, i.e., we have access to polymer foams that only differ in their polydispersity.Item Open Access Adjustable polystyrene nanoparticle templates for the production of mesoporous foams and ZnO inverse opals(2020) Abitaev, Karina; Qawasmi, Yaseen; Atanasova, Petia; Dargel, Carina; Bill, Joachim; Hellweg, Thomas; Sottmann, ThomasThe manifold applications of porous materials, such as in storage, separation, and catalysis, have led to an enormous interest in their cost-efficient preparation. A promising strategy to obtain porous materials with adjustable pore size and morphology is to use templates exhibiting the appropriate nanostructure. In this study, close-packed polystyrene (PS) nanoparticles, synthesized by emulsion polymerization, were used to produce porous PS and ZnO inverse opals. The size and distribution of the polystyrene nanoparticles, characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), and scanning electron microscopy (SEM), were controlled via the concentration of sodium dodecyl sulfate (SDS). Systematic measurements of the water/styrene-interfacial tension show that the critical micelle concentration (CMC) of the ternary water–styrene–SDS system, which determines whether monodisperse or polydisperse PS particles are obtained, is considerably lower than that of the binary water–SDS system. The assemblies of close-packed PS nanoparticles obtained via drying were then studied by small-angle X-ray scattering (SAXS) and SEM. Both techniques prove that PS nanoparticles synthesized above the CMC result in a significantly unordered but denser packing of the particles. The polystyrene particles were subsequently used to produce porous polystyrene and ZnO inverse opals. While the former consists of micrometer-sized spherical pores surrounded by extended open-cellular regions of mesopores (Rpore ≈ 25 nm), the latter are made of ZnO-nanoparticles forming a structure of well-aligned interconnected pores.Item Open Access Chemical design and probing of novel molecular 2-qubit systems(2023) Schäfter, Dennis; Slageren, Joris van (Prof. Dr.)Item Open Access Molekulardynamische Simulation zu Fragen der smektischen Translationsordnung in thermotropen Flüssigkristallen(2021) Häge, Christian; Gießelmann, Frank (Prof. Dr.)Es wurden zwei Fragestellungen zur smektischen Translationsordnung von Flüssigkristallen bearbeitet. Der erste Teil der Arbeit befasst sich mit dem Einfluss der molekularen Ladungsanordnung von ionischen Flüssigkristallen auf deren Phasenverhalten. Der zweite Teil der Arbeit untersucht unter welchen Voraussetzungen die Gleichungen zur Bestimmung von Translationsordnungsparametern angewendet werden können und welche Rolle die molekulare Elektronendichteverteilung des Mesogens dabei spielt.Item Open Access Porous polymers via emulsion templating : pore deformation during solidification cannot be explained by an osmotic transport!(2020) Koch, Lukas; Drenckhan, Wiebke; Stubenrauch, CosimaUsing microfluidics, we were able to synthesize monodisperse water-in-monomer emulsions with styrene and divinylbenzene (DVB) as monomers. When polymerizing and drying these emulsions, we found that the structure of the resulting macroporous polymer strongly depends on the type of initiator. With the oil-soluble azobisisobutyronitrile (AIBN), an open-cell structure with spherical pores was obtained. However, with the water-soluble potassium peroxydisulfate (KPS), a closed-cell structure with rhombic dodecahedron-shaped pores and thick, layered pore walls was formed. In the latter case, a yet unexplained mechanism counteracts the capillary pressure arising from surface minimization: the surface area of a rhombic dodecahedron is ~ 10% larger than that of a sphere. In our previous work, we suggested that the underlying mechanism may be osmotic transport of DVB from the plateau borders to the films. We argued that this transport also explains the layered pore walls, i.e., the formation of two outer poly-DVB-rich layers and one inner polystyrene-rich layer. In order to prove or disprove this mechanism, we carried out additional experiments. However, none of those experiments corroborated our hypothesis of osmotic transport! This study provides clear experimental evidence that our previously suggested mechanism via which spherical droplets become polyhedral pores is incorrect. We will describe (a) the rationale behind the additional experiments, (b) our expectations, and (c) our findings. Last but not least, we will discuss all of this in the light of the proposed osmotic transport.Item Open Access Macrocyclization of dienes under confinement with cationic tungsten imido/oxo alkylidene N‐heterocyclic carbene complexes(2023) Ziegler, Felix; Bruckner, Johanna R.; Nowakowski, Michal; Bauer, Matthias; Probst, Patrick; Atwi, Boshra; Buchmeiser, Michael R.Macrocyclization reactions are still challenging due to competing oligomerization, which requires the use of small substrate concentrations. Here, the cationic tungsten imido and tungsten oxo alkylidene N-heterocyclic carbene complexes [[W(N-2,6-Cl2-C6H3)(CHCMe2Ph(OC6F5)(pivalonitrile)(IMes)+ B(ArF)4-] (W1) and [W(O (CHCMe2Ph(OCMe(CF3)2)(IMes)(CH3CN)+ B(ArF)4-] (W2) (IMes=1,3-dimesitylimidazol-2-ylidene; B(ArF)4-=tetrakis(3,5-bis(trifluoromethyl)phenyl borate) have been immobilized inside the pores of ordered mesoporous silica (OMS) with pore diameters of 3.3 and 6.8 nm, respectively, using a pore-selective immobilization protocol. X-ray absorption spectroscopy of W1@OMS showed that even though the catalyst structure is contracted due to confinement by the mesopores, both the oxidation state and structure of the catalyst stayed intact upon immobilization. Catalytic testing with four differently sized α,ω-dienes revealed a dramatically increased macrocyclization (MC) and Z-selectivity of the supported catalysts compared to the homogenous progenitors, allowing high substrate concentrations of 25 mM. With the supported complexes, a maximum increase in MC-selectivity from 27 to 81 % and in Z-selectivity from 17 to 34 % was achieved. In general, smaller mesopores exhibited a stronger confinement effect. A comparison of the two supported tungsten-based catalysts showed that W1@OMS possesses a higher MC-selectivity, while W2@OMS exhibits a higher Z-selectivity which can be rationalized by the structures of the catalysts.Item Open Access Dynamic ultrasound projector controlled by light(2022) Ma, Zhichao; Joh, Hyungmok; Fan, Donglei Emma; Fischer, PeerDynamic acoustic wavefront control is essential for many acoustic applications, including biomedical imaging and particle manipulation. Conventional methods are either static or in the case of phased transducer arrays are limited to a few elements and hence limited control. Here, a dynamic acoustic wavefront control method based on light patterns that locally trigger the generation of microbubbles is introduced. As a small gas bubble can effectively stop ultrasound transmission in a liquid, the optical images are used to drive a short electrolysis and form microbubble patterns. The generation of microbubbles is controlled by structured light projection at a low intensity of 65 mW cm-2 and only requires about 100 ms. The bubble pattern is thus able to modify the wavefront of acoustic waves from a single transducer. The method is employed to realize an acoustic projector that can generate various acoustic images and patterns, including multiple foci and acoustic phase gradients. Hydrophone scans show that the acoustic field after the modulation by the microbubble pattern forms according to the prediction. It is believed that combining a versatile optical projector to realize an ultrasound projector is a general scheme, which can benefit a multitude of applications based on dynamic acoustic fields.Item Open Access Magnetic tilting in nematic liquid crystals driven by self‐assembly(2021) Hähsler, Martin; Nádasi, Hajnalka; Feneberg, Martin; Marino, Sebastian; Giesselmann, Frank; Behrens, Silke; Eremin, AlexeySelf‐assembly is one of the crucial mechanisms allowing the design multifunctional materials. Soft hybrid materials contain components of different natures and exhibit competitive interactions which drive self‐organization into structures of a particular function. Here a novel type of a magnetic hybrid material where the molecular tilt can be manipulated through a delicate balance between the topologically‐assisted colloidal self‐assembly of magnetic nanoparticles and the anisotropic molecular interactions in a liquid crystal matrix is demonstrated.Item Open Access Probing molecular quantum bits(2021) Lenz, Samuel; Slageren, Joris van (Prof. Dr.)