Universität Stuttgart
Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1
Browse
84 results
Search Results
Item Open Access Integrating a dynamic central metabolism model of cancer cells with a hybrid 3D multiscale model for vascular hepatocellular carcinoma growth(2022) Lapin, Alexey; Perfahl, Holger; Jain, Harsh Vardhan; Reuss, MatthiasWe develop here a novel modelling approach with the aim of closing the conceptual gap between tumour-level metabolic processes and the metabolic processes occurring in individual cancer cells. In particular, the metabolism in hepatocellular carcinoma derived cell lines (HEPG2 cells) has been well characterized but implementations of multiscale models integrating this known metabolism have not been previously reported. We therefore extend a previously published multiscale model of vascular tumour growth, and integrate it with an experimentally verified network of central metabolism in HEPG2 cells. This resultant combined model links spatially heterogeneous vascular tumour growth with known metabolic networks within tumour cells and accounts for blood flow, angiogenesis, vascular remodelling and nutrient/growth factor transport within a growing tumour, as well as the movement of, and interactions between normal and cancer cells. Model simulations report for the first time, predictions of spatially resolved time courses of core metabolites in HEPG2 cells. These simulations can be performed at a sufficient scale to incorporate clinically relevant features of different tumour systems using reasonable computational resources. Our results predict larger than expected temporal and spatial heterogeneity in the intracellular concentrations of glucose, oxygen, lactate pyruvate, f16bp and Acetyl-CoA. The integrated multiscale model developed here provides an ideal quantitative framework in which to study the relationship between dosage, timing, and scheduling of anti-neoplastic agents and the physiological effects of tumour metabolism at the cellular level. Such models, therefore, have the potential to inform treatment decisions when drug response is dependent on the metabolic state of individual cancer cells.Item Open Access Constitutive correlations for mass transport in fibrous media based on asymptotic homogenization(2023) Maier, Lukas; Kufferath-Sieberin, Lars; Pauly, Leon; Hopp-Hirschler, Manuel; Gresser, Götz T.; Nieken, UlrichMass transport in textiles is crucial. Knowledge of effective mass transport properties of textiles can be used to improve processes and applications where textiles are used. Mass transfer in knitted and woven fabrics strongly depends on the yarn used. In particular, the permeability and effective diffusion coefficient of yarns are of interest. Correlations are often used to estimate the mass transfer properties of yarns. These correlations commonly assume an ordered distribution, but here we demonstrate that an ordered distribution leads to an overestimation of mass transfer properties. We therefore address the impact of random ordering on the effective diffusivity and permeability of yarns and show that it is important to account for the random arrangement of fibers in order to predict mass transfer. To do this, Representative Volume Elements are randomly generated to represent the structure of yarns made from continuous filaments of synthetic materials. Furthermore, parallel, randomly arranged fibers with a circular cross-section are assumed. By solving the so-called cell problems on the Representative Volume Elements, transport coefficients can be calculated for given porosities. These transport coefficients, which are based on a digital reconstruction of the yarn and asymptotic homogenization, are then used to derive an improved correlation for the effective diffusivity and permeability as a function of porosity and fiber diameter. At porosities below 0.7, the predicted transport is significantly lower under the assumption of random ordering. The approach is not limited to circular fibers and may be extended to arbitrary fiber geometries.Item Open Access Dynamic modelling of multitubular catalytic reactors(1991) Stankiewicz, Andrzej; Eigenberger, GerhartThis paper presents a study on modelling and simulation of transient operational characteristics in multitubular fixed-bed reactors. The dynamic model of the reactor is based on a porous body approach which regards the intertubular space as a pseudo-homogeneous environment. Such an approach permits to take into account most factors in the geometrical design of the unit and thus to study the influence of various shell-side geometrical and operational parameters on the reactor behaviour. Based on the model, the dynamic responses of the two most common industrial reactor designs, i.e. the parallel flow unit with distributing plates and the crossflow reactor with disk-and-doughnut baffles have been investigated and compared. In addition, some problems of correct space discretization and use of time-dependent regridding procedures, are discussed.Item Open Access Membrane electrode assembly for water electrolysis(2023) Nguyen, Thi Hai Van; Friedrich, K. Andreas (Prof. Dr. rer. nat.)Maintaining a sufficient energy supply while minimizing the impact on the environment and climate is one of the greatest social and scientific challenges of our times. There are various fields of research and technological developments in the context of global warming and limitless growing energy demand, and the focus of this PhD programme is on artificial photosynthesis, more specifically on the assembly of Membrane electrode assembly for water electrolyzer part. Mimicking photosynthesis in a scheme to trap solar energy in chemical bonds (fuels) is a scientific and technological challenge. Having a cost-effective and reliable process stays one of the main limitations in order to achieving the long-term goal of this approach. In this work, within the European eSCALED project, the elaboration of Membrane Electrode Assembly (MEA) for water electrolysis by introducing new materials and low-cost fabrication methods was investigated.Item Open Access Synthese und Charakterisierung teilfluorierter Poly(aryl)-Ionomere als Polymerelektrolytmembranen für Brennstoffzellen und ESR-spektroskopische Untersuchung der radikalinduzierten Degradation von Modellverbindungen(2008) Schönberger, Frank; Roduner, Emil (Prof. Dr.)Im ersten Teil dieser Arbeit werden zunächst verschiedene Strategien zum Aufbau sulfonierter teilfluorierter Poly(aryl)e entwickelt und synthetisch umgesetzt. Konzeptionell liegt dabei die Hypothese zugrunde, dass sich teilfluorierte Poly(aryl)-Ionomere gegenüber nichtfluorierten durch eine erhöhte Acidität auszeichnen. Außerdem weisen sie eine höhere Bindungsdissoziationsenergie sowohl der C-F-Bindungen als auch der benachbarten C-H-Bindungen auf, womit ein Gewinn an radikalischer und somit chemischer und thermischer Stabilität einhergeht. Um den Einfluss der chemischen Struktur der jeweiligen (teilfluorierten) Monomerbausteine zu untersuchen, werden zunächst homo-Polymere mit verschiedenen Struktureinheiten (mit aromatischen C-F-Bindungen, C(CF3)2-verbrückten und CF3-substitutierten Phenylenringen) durch Polykondensation synthetisiert und charakterisiert (Elementaranalyse, NMR-Spektroskopie, Gelpermeationschromatographie). Zur gezielten Synthese der Monomere werden bekannte organische Reaktionen, wie die Balz-Schiemann-Reaktion, Suzuki-Reaktion und die Ullmann-Biarylsynthese, angewandt. Nach Sulfonierung der homo-Polymere werden (ionisch-vernetzte) Membranen hergestellt und hinsichtlich Eignung als Polymerelektrolytmembran für Brennstoffzellen charakterisiert (Ionenaustauscherkapazität, Protonenleitfähigkeit, thermische und chemische Stabilität, Wasseraufnahme, Längenänderung). Neben der chemischen Natur der Monomere ist auch deren Anordnung im Polymer bzw. Ionomer für die Eigenschaften der hergestellten Membranen wichtig. Aus diesem Grunde werden mikrophasenseparierte Block-co-Ionomere, ausgehend von hydrophilen (sulfonierten) und hydrophoben (teilfluorierten) telechelen Makromonomeren, synthetisiert und charakterisiert. Dabei werden sowohl der Einfluss der jeweiligen Blocklänge als auch der chemischen Natur der eingesetzten Monomere auf die Membraneigenschaften vergleichend untersucht. Auf der Grundlage der in diesem Teil der Arbeit gewonnen Erkenntnisse werden die Vor- und Nachteile teilfluorierter Ionomermembranen analysiert und diskutiert. Der zweite Teil der Arbeit befasst sich mit der ESR-spektroskopischen Untersuchung der radikalinduzierten Degradation von Modellverbindungen, denen Struktureinheiten einiger im ersten Teil der Arbeit hergestellten Poly(aryl)-Ionomere entsprechen. Diese Modellverbindungen werden in einer Durchflusszelle Hydroxyl- und Hydroperoxylradikalen ausgesetzt, welche direkt im Hohlraumresonator eines ESR-Spektrometers durch Photolyse von Wasserstoffperoxid erzeugt werden. Mit diesem Aufbau können verschiedene Parameter (wie die Hydroxylradikal- und Monomerkonzentration, die Durchflussrate und der pH-Wert) gezielt variiert werden und so deren Einflüsse in Bezug auf die Produktbildung der aromatischen Modellverbindungen mit den Hydroxylradikalen abgeschätzt werden. Aus diesen Untersuchungen lassen sich Rückschlüsse auf mögliche Radikalreaktionen des Poly(aryl)-Ionomers ziehen und damit Aussagen in Bezug auf zu vermeidende strukturelle Merkmale (z.B. Art der Endgruppen der Ionomere) und zu vermeidende Bedingungen (z.B. pH-Wertschwankungen in der Membran) treffen.Item Open Access Convective drying of porous media : comparison of phase-field simulations with microfluidic experiments(2024) Maier, Lukas; Brosch, Sebastian; Gaehr, Magnus; Linkhorst, John; Wessling, Matthias; Nieken, UlrichConvective drying of porous media is central to many engineering applications, ranging from spray drying over water management in fuel cells to food drying. To improve these processes, a deep understanding of drying phenomena in porous media is crucial. Therefore, detailed simulation of multiphase flows with phase change is of great importance to investigate the complex processes involved in drying porous media. While many studies aim to access the phenomena solely by simulations, here we succeed to compare comprehensively simulations with an experimental methodology based on microfluidic multiphase flow studies in engineered porous media. In this contribution, we propose a Navier-Stokes Cahn-Hilliard model coupled with balance equations for heat and moisture to simulate the two-phase flow with phase change. The phase distribution of the two fluids air and water is modeled by the Phase-Field equation. Comparisons with experiments are rare in the literature and usually involve very simple cases. We compare our simulation with convective drying experiments of porous media. Experimentally, the interface propagation of the water-air interface was visualized in detail during drying in a structured microfluidic cell made from PDMS. The drying pattern and the drying time in the experiment are very well reproduced by our simulation. This validation will enable the application for the presented Navier-Stokes Cahn-Hilliard model in more complex cases focused more on applications, e.g., in the field of fibrous materials.Item Open Access Synthesis and characterization of novel perfluoro aromatic side chain sulfonated PSU ionomers(2024) Martschin, Philipp; Atanasov, Vladimir; Thiele, Simon; Kerres, JochenPolyethersulfone (PSU) as a commercially available polymer offers many different opportunities for functionalization for diverse fields of application, for example, electrophilic substitutions like sulfonation and bromination or nucleophilic reactions such as lithiation. This study presents three different polysulfone derivatives, first functionalized by a lithiation reaction, followed by a reaction with carbonyl compounds containing pentafluorophenyl groups. In the last step, the pentafluorophenyl moieties of the modified PSU were sulfonated by thiolation and subsequent oxidation to sulfonic acid groups. Those novel PSU derivatives were characterized by NMR, DSC, TGA, GPC, and titration. Based on these ionomers, we show the fabrication of pure and acid-base blend membranes with promising proton conductivities. These novel sulfonic acid groups containing materials are potentially promising candidates for membranes or ionomers in electrochemical applications such as proton exchange membrane fuel cells (PEMFCs), proton exchange membrane water electrolysis (PEMWEs), or redox flow batteries (RFBs).Item Open Access H+-conducting aromatic multiblock copolymer and blend membranes and their application in PEM electrolysis(2021) Bender, Johannes; Mayerhöfer, Britta; Trinke, Patrick; Bensmann, Boris; Hanke-Rauschenbach, Richard; Krajinovic, Katica; Thiele, Simon; Kerres, JochenAs an alternative to common perfluorosulfonic acid-based polyelectrolytes, we present the synthesis and characterization of proton exchange membranes based on two different concepts: (i) Covalently bound multiblock-co-ionomers with a nanophase-separated structure exhibit tunable properties depending on hydrophilic and hydrophobic components’ ratios. Here, the blocks were synthesized individually via step-growth polycondensation from either partially fluorinated or sulfonated aromatic monomers. (ii) Ionically crosslinked blend membranes of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones combine the hydrophilic component’s high proton conductivities with high mechanical stability established by the hydrophobic components. In addition to the polymer synthesis, membrane preparation, and thorough characterization of the obtained materials, hydrogen permeability is determined using linear sweep voltammetry. Furthermore, initial in situ tests in a PEM electrolysis cell show promising cell performance, which can be increased by optimizing electrodes with regard to binders for the respective membrane material.Item Open Access Synthesis and characterization of anion exchange blend membranes for vanadium redox flow battery applications(2021) Cho, Hyeongrae; Friedrich, K. Andreas (Prof. Dr. rer. nat.)In this dissertation, Anion Exchange Blend Membranes (AEBMs) were synthesized and applied in Vanadium Redox Flow Batteries (VRFBs). In the first paper, AEBMs were systematically optimized for VRFBs by varying the composition of polymers components. A bromomethylated poly (2, 6-dimethyl-1,4-phenylene oxide) (Br-PPO) was used as an anionic exchange precursor which was quaternized with 1,2,4,5-tetramethylmidazole (TMIm). A Polybenzimidazole-OO (PBI-OO, produced by Fuma-Tech) was used as a matrix polymer to provide mechanical strength. A minor amount of sulfonated polymer was used as an ionical cross-linker. Those AEBMs showed comparable Energy Efficiency (EE) with Nafion 212 membranes and one of the synthesized AEBMs (BM-TMIm 4) showed a superior Coulombic Efficiency (CE) of almost no decreasing after 300 charging-discharging cycles with a significant capacity retention of 77% of the initial value for after 300 charging-discharging cycles at a current density of 40 mA/cm2. Therefore, AEBMs are promising candidates for long-term operation in VRFBs if the proportion and type of the different components in the blend system is carefully adjusted. In the first paper, the composition of AEBMs were optimized for use in VRFBs. In the second paper, AEBMs were prepared with different polymer combinations. These AEBMs consisted of 3 polymer components. 1) F6-PBI (fluorinated PBI) or PBI-OO (non-fluorinated PBI): PBI was used as a matrix polymer, 2) Br-PPO: Br-PPO was used as an anion exchange polymer precursor by quaternizing with TMIm to provide anion exchange sites, 3) a partially fluorinated polyether or a non-fluorinated poly (ether sulfone): sulfonated polymer was used as an ionical cross-linker. The same weight ratios of three components were used in blend membranes, while different combinations of polymers were used. Similar properties of blend membranes such as ion exchange capacity, conductivity and swelling behavior showed since same amount of anion exchange polymer in each blend membrane was used. In VRFB test, all blend membranes showed better performances than the commercial membranes (Nafion: a cation exchange membrane and FAP 450: an anion exchange membrane) in terms of coulombic-, voltage- and energy efficiencies. One of the blend membranes (BM-TMIm4 FF), which is composed fluorinated polymers, exhibited excellent capacity retention showing no capacity decay over 550 charging-discharging cycles run at a current density of 40 mA/cm2. The outstanding performance of fluorinated polymers-based blend membranes probably is due to the highly stability of F6-PBI in an acidic condition. A pure F6-PBI membrane showed no structural changes in 30 % sulfuric acid solution for 9 days confirmed by Fourier-Transfrom Infrared Spectroscopy (FT-IR spectra), while a PBI-OO membrane was sulfonated after few days. Thus, it can be concluded that if proper matrix polymer chosen for blend membrane, the AEBMs in VRFBs are expected to exhibit superior performance. In the paper 3, AEBMs were synthesized by 3 steps based on Poly(pentafluorostyrene) (PPFSt) for use in VRFBs. Firstly, 1-(2-dimethylaminoethyl)-5-mercaptotetrazole was grafted onto PPFSt by nucleophilic substitution on the para-position. Secondly, the tertiary amino groups were quaternized with iodomethane to provide anion exchange sites. Thirdly, AEBMs were fabricated by blending of synthesized anion exchange polymer with F6-PBI. The blend membrane containing of 30% F6PBI showed better VRFBs performance that Nafion membrane in terms of energy efficiency, Open Circuit Voltage (OCV) and charging-discharging cycling. While the blend membrane containing of 40% F6-PBI displayed much longer OCV time and capacity retention by a charging-discharging test than that of Nafion membrane. It can be concluded that AEBMs are strong candidate for VRFB applications. The AEBMs tested in VRFBs have shown better performances than that of commercial reference membranes of a cation exchange membrane (Nafion) and an anion exchange membrane (FAP 450). By considering the battery test results of AEBMs in this study, therefore, it can be concluded that the AEBMs are very promising candidates as separators in VRFBs if the matrix polymer is chosen properly. One further potential application of those blend membranes can be used in phosphoric acid doped high temperature proton exchange membrane fuel cells (PA-doped HT-PEMFCs), since the AEBMs in this dissertation showed high thermal stability. In recent paper (Nat Energy 1, 16120 (2016)), anion exchange membrane showed very promising results in PA-doped PEMFCs displaying much better performances than that of a polybenzimidazole membrane (a standard membrane for PA-doped HT-PEMFCs) in the FC test. The results in our patent have shown also that those anion exchange membranes exhibited promising performances in the fuel cell test. Therefore, anion exchange blend membranes synthesized in this study are expected to excellent performances for phosphoric acid doped HT-PEMFCs.Item Open Access Thin organic‐inorganic anti‐fouling hybrid‐films for microreactor components(2022) Neßlinger, Vanessa; Welzel, Stefan; Rieker, Florian; Meinderink, Dennis; Nieken, Ulrich; Grundmeier, GuidoDeposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well‐known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra‐thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol‐gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti‐adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X‐ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field‐emission scanning electron microscopy (FE‐SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film‐coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.