Publikationen - Mikroskopie an Polymersystemen - Microscopy on Polymer Systems by Ralf and Yi Thomann

Universität Freiburg	Veröffentlichungen - Dr. Yi Thomann 2010-2025
84: Abiotic Acyl Transfer Cascades Driven by Aminoacyl Phosphate Esters and Self-Assembly Mahesh D Pol, Ralf Thomann, Yi Thomann, Charalampos G Pappas J. Am. Chem. Soc. 2024, 146, 43, 29621-29629 doi.org/10.1021/jacs.4c10082 Abstract: Biochemical acyl transfer cascades, such as those initiated by the adenylation of carboxylic acids, are central to various biological processes, including protein synthesis and fatty acid metabolism. Designing cascade reactions in aqueous media remains challenging due to the need to control multiple, sequential reactions in a single pot and manage the stability of reactive intermediates. Herein, we developed abiotic cascades using aminoacyl phosphate esters, the synthetic counterparts of biological aminoacyl adenylates, to drive sequential chemical reactions and self-assembly in a single pot. We demonstrated that the structural elements of amino acid side chains (aromatic versus aliphatic) significantly influence the reactivity and half-lives of aminoacyl phosphate esters, ranging from hours to days. This behavior, in turn, affects the number of couplings we can achieve in the network and the self-assembly propensity of activated intermediate structures. The cascades are constructed using bifunctional peptide substrates featuring side chain nucleophiles. Specifically, aromatic amino acids facilitate the formation of transient thioesters, which preorganized into spherical aggregates and further couple into chimeric assemblies composed of esters and thioesters. In contrast, aliphatic amino acids, which lack the ability to form such structures, predominantly undergo hydrolysis, bypassing further transformations after thioester formation. Additionally, in mixtures containing multiple aminoacyl phosphate esters and peptide substrates, we achieved selective product formation by following a distinct pathway that favors subsequent reactions through reactivity changes and self-assembly. By coupling chemical reactions with molecules of varying reactivity time scales, we can drive multiple reaction clocks with distinct lifetimes and self-assembly dynamics, facilitating precise temporal and structural regulation. 83: Microstructure of selective laser melted 316L under non-equilibrium solidification conditions EF Özel, D Pede, C Müller, Y Thomann, R Thomann, H Mozaffari-Jovein Journal of Experimental and Theoretical Analyses 1 (2), 64-73, 2023 doi.org/10.3390/jeta1020005 Abstract: In this study, the microstructural properties of selective laser melted 316L stainless steel were investigated using optical, scanning and transmission electron microscopy as well as X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy. The results show a very fine microstructure with visible melt pool boundaries and austenite as the predominant phase. Extremely fine sub-grain structures can be found within the grains, consisting of colonies of round or elongated cellular structures depending on orientations. Due to the prevailing cooling and solidification conditions, micro-segregations occur, leading to enrichment of the sub-grain boundaries with alloying elements such as silicon, chromium, manganese and molybdenum. The presence of ferrite could be detected in this area using TEM analysis. 82: High-Resolution Patterning of Organic-Inorganic Photoresins for Tungsten and Tungsten Carbide Microstructures Manuel Luitz, Diana Pellegrini, Miriam von Holst, Khaled Seteiz, Lukas Gröner, Mario Schleyer, Michael Daub, Andreas Warmbold, Yi Thomann, Ralf Thomann, Frederik Kotz-Helmer, Bastian E Rapp Advanced Engineering Materials 25 (13), 2201927, 2023 doi.org/10.1002/adem.202201927 Abstract: Tungsten is an important material for high-temperature applications due to its high chemical and thermal stability. Its carbide, that is, tungsten carbide, is used in tool manufacturing because of its outstanding hardness and as a catalyst scaffold due to its morphology and large surface area. However, microstructuring, especially high-resolution 3D microstructuring of both materials, is a complex and challenging process which suffers from slow speeds and requires expensive specialized equipment. Traditional subtractive machining methods, for example, milling, are often not feasible because of the hardness and brittleness of the materials. Commonly, tungsten and tungsten carbide are manufactured by powder metallurgy. However, these methods are very limited in the complexity and resolution of the produced components. Herein, tungsten ion-containing organic-inorganic photoresins, which are patterned by two-photon lithography (TPL) at micrometer resolution, are introduced. The printed structures are converted to tungsten or tungsten carbide by thermal debinding and reduction of the precursor or carbothermal reduction reaction, respectively. Using TPL, complex 3D tungsten and tungsten carbide structures are prepared with a resolution down to 2 and 7??m, respectively. This new pathway of structuring tungsten and its carbide facilitates a broad range of applications from micromachining to metamaterials and catalysis. 81: µ-CT Untersuchungen an heimischen Holzarten Yi Thomann, Ralf Thomann Poster - Zenodo, Published April 4, 2022 doi.org/10.5281/zenodo.6414287 Abstract: µ-CT an Kiefer, Eiche, Linde, Zwetschgenholz, Robinie, Rotbuche, Platane 80: The mineralization of various 3d-printed pcl composites Artem Egorov, Bianca Riedel, Johannes Vinke, Hagen Schmal, Ralf Thomann, Yi Thomann, Michael Seidenstuecker J. Funct. Biomater. 2022, 13(4), 238 doi.org/10.3390/jfb13040238 Abstract: In this project, different calcification methods for collagen and collagen coatings were compared in terms of their applicability for 3D printing and production of collagen-coated scaffolds. For this purpose, scaffolds were printed from polycaprolactone PCL using the EnvisionTec 3D Bioplotter and then coated with collagen. Four different coating methods were then applied: hydroxyapatite (HA) powder directly in the collagen coating, incubation in 10× SBF, coating with alkaline phosphatase (ALP), and coating with poly-L-aspartic acid. The results were compared by ESEM, µCT, TEM, and EDX. HA directly in the collagen solution resulted in a pH change and thus an increase in viscosity, leading to clumping on the scaffolds. As a function of incubation time in 10× SBF as well as in ALP, HA layer thickness increased, while no coating on the collagen layer was apparently observed with poly-L-aspartic acid. Only ultrathin sections and TEM with SuperEDX detected nano crystalline HA in the collagen layer. Exclusively the incubation in poly-L-aspartic acid led to HA crystals within the collagen coating compared to all other methods where the HA layers formed in different forms only at the collagen layer. 79: Laser Ablation on Isostatic Graphite-A New Way to Create Exfoliated Graphite Maria Isabel Sierra-Trillo, Ralf Thomann, Ingo Krossing, Ralf Hanselmann, Rolf Mülhaupt, Yi Thomann Materials 15 (16), 5474, 2022 doi.org/10.3390/ma15165474 Abstract: In search of a new way to fabricate graphene-like materials, isostatic graphite targets were ablated using high peak power with a nanosecond-pulsed infrared laser. We conducted dry ablations in an argon atmosphere and liquid-phase ablations in the presence of a liquid medium (water or toluene). After the dry ablation, the SEM images of the target showed carbon in the form of a volcano-like grain structure, which seemed to be the result of liquid carbon ejected from the ablation center. No graphite exfoliation could be achieved using dry ablation. When using liquid phase ablation with water or toluene as a liquid medium, no traces of the formation of liquid carbon were found, but cleaner and deeper craters were observed. In particular, when using toluene as a liquid medium, typical graphite exfoliation was found. We believe that due to the extremely high pressure and high temperature induced by the laser pulses, toluene was able to intercalate into the graphite layers. Between the laser pulses, the intercalated toluene was able to flash evaporate and blow-up the graphite, which resulted in exfoliated graphite. Exfoliated graphite was found on the ablated graphite surface, as well as in the toluene medium. The ablation experiments with toluene undertaken in this study demonstrated an effective method of producing micrometer-sized graphene material. When using water as a liquid medium, no massive graphite exfoliation was observed. This meant that under the used laser conditions, toluene was a better intercalant for graphite exfoliation than water. 78: An Artificial SEI Layer Based on an Inorganic Coordination Polymer with Self-Healing Ability for Long-Lived Rechargeable Lithium-Metal Batteries Witali Beichel, Julian Skrotzki, Petra Klose, Christian Njel, Burkhard Butschke, Stephan Burger, Lili Liu, Ralf Thomann, Yi Thomann, Daniel Biro, Simon Thiele, Ingo Krossing Batteries + supercaps 5 (2), e202100347, 2022 doi.org/10.1002/batt.202100347 Abstract: Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20 M dimethoxyethane-solution of the phosphoric acid derivative (CF3CH2O)2P(O)OH (HBFEP), an artificial solid electrolyte interphase (SEI) is generated on the Li-metal surface. Hence, HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li-ion conducting inorganic coordination polymer. This film exhibits - due to the reversibly breaking ionic bonds - self-healing ability upon cycling-induced volume expansion of Li. The presence of LiBFEP as the major component in the artificial SEI is proven by ATR-IR and XPS measurements. SEM characterization of HBFEP-treated Li samples reveals porous layers on top of the Li surface with at least 3 ?m thickness. Li?Li symmetrical cells with HBFEP-modified Li electrodes show a three- to almost fourfold cycle-lifetime increase at 0.1 mA cm?2 in a demanding model electrolyte that facilitates fast battery failure (1 M LiOTf in TEGDME). Hence, the LiBFEP-enriched layer apparently acts as a Li-ion conducting protection barrier between Li and the electrolyte, enhancing the rechargeability of Li electrodes. 77: Facile fabrication of micro-/nanostructured, superhydrophobic membranes with adjustable porosity by 3D printing Fadoua Mayoussi, Egan H Doeven, Andrea Kick, Andreas Goralczyk, Yi Thomann, Patrick Risch, Rosanne M Guijt, Frederik Kotz, Dorothea Helmer, Bastian E Rapp J. Mater. Chem. A, 2021, 9, 21379-21386 doi.org/10.1039/D1TA03352B Abstract: Porous membranes with special wetting properties have attracted great interest due to their various functions and wide applications, including water filtration, selective oil/water separation and oil skimming. Special wetting properties such as superhydrophobicity can be achieved by controlling the surface chemistry as well as the surface topography of a substrate. Three-dimensional (3D) printing is a promising method for the fast and easy generation of various structures. The most common method for 3D printing of superhydrophobic materials is a two-step fabrication process: 3D printing of user-defined topographies, such as surface structures or bulk porosity, followed by a chemical post-processing with low-surface energy chemicals such as fluorinated silanes. Another common method is using a hydrophobic polymer ink to print intricate surface structures. However, the resolution of most common printers is not sufficient to produce nano-/microstructured textures, moreover, the resulting delicate surface micro- or nanostructures are very prone to abrasion. Herein, we report a simple approach for 3D printing of superhydrophobic micro-/nanoporous membranes in a single step, combining the required topography and chemistry. The bulk porosity of this material, which we term "Fluoropor", makes it insensitive to abrasion. To achieve this, a photocurable fluorinated resin is mixed with a porogen mixture and 3D printed using a stereolithography (SLA) printing process. This way, micro-/nanoporous membranes with superhydrophobic properties with static contact angles of 164° are fabricated. The pore size of the membranes can be adjusted from 30 nm to 300 nm by only changing the porogen ratio in the mixture. We show the applicability of the printed membranes for oil/water separation and the formation of Salvinia layers which are of great interest for drag reduction in maritime transportation and fouling prevention. 76: Analysis of the Growth of Laterally Aligned SnO2 Nanowires by Thermodynamic Considerations and Experiments Jasmin-Clara Bürger, Sebastian Gutsch, Yi Thomann, Ralf Thomann, Bjoern Christian, Oliver Ambacher, Margit Zacharias Cryst. Growth Des. 2021, 21, 1, 191-199 doi.org/10.1021/acs.cgd.0c00983 Abstract: Recently, we reported the experimental tuning of the growth of freestanding SnO2 nanowires to a laterally aligned nanowire growth mode. Here, we present thermodynamic considerations taking into account the previously reported influencing parameters determining the experiments, i.e., the total pressure, the Sn/O ratio at the sample sites, the nanowire diameter, and the substrate type. We will discuss process parameters which will prefer a laterally aligned growth mode. We show that a continuous gold film used as catalyst inhibits the laterally aligned growth. Only at the edges the lateral growth can proceed, whereas the area region is covered by freestanding wires. The reason for that will be explained in a model. Furthermore, the laterally aligned nanowire surface faceting is analyzed by means of transmission electron microscopy and atomic force microscopy and explained. 75: The Scissors Effect in Action: The Fox-Flory Relationship between the Glass Transition Temperature of Crosslinked Poly(Methyl Methacrylate) and Mc in Nanophase Separated Poly(Methyl Methacrylate)-l-Polyisobutylene Conetworks Szabolcs Pásztor, Bálint Becsei, Györgyi Szarka, Yi Thomann, Ralf Thomann, Rolf Mühlhaupt, Béla Iván Materials 2020, 13(21), 4822 doi.org/10.3390/ma13214822 Abstract: The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox-Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox-Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,? ? K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5-20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials. 74: Nanoconfined Crosslinked Poly(ionic liquid)s with Unprecedented Selective Swelling Properties Obtained by Alkylation in Nanophase-Separated Poly(1-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks Tímea Stumphauser, György Kasza, Attila Domján, András Wacha, Zoltán Varga, Yi Thomann, Ralf Thomann, Balázs Pásztói, Tobias M. Trötschler, Benjamin Kerscher, Rolf Mülhaupt and Béla Iván Polymers 2020, 12(10), 2292 doi.org/10.3390/polym12102292 Abstract: Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15-20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2-8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields. 73: Melt-Processable Nacre-Mimetic Hydrocarbon Composites via Polymer 1D Nanostructure Formation F. Zhong, R. Thomann, Y. Thomann, L. Burk, R. Mülhaupt Macromolecules 2019, 52, 23, 9272-9279 doi.org/10.1021/acs.macromol.9b01184 Abstract: Nacre-mimicking layered organic/inorganic hybrid materials exhibiting ultrahigh stiffness and strength frequently require multistep processing that is restricted to polar and even water-soluble polymers. Herein, nacre-mimetic hydrocarbon composites were fabricated by single-step injection molding. The key intermediates are organophilic ultrathin ?-Al(OH)3 (O-gibbsite) single-crystal nanoplatelets and all-hydrocarbon composites (All-PE) containing aligned, extended-chain ultrahigh-molecular-weight polyethylene (UHMWPE) as one-dimensional (1D) nanostructures embedded in a polyethylene (PE) matrix. This formation of flow-induced UHMWPE 1D nanostructures mimics chitin nanofibers in nacre and drives the alignment of O-gibbsite nanoplatelets to assemble bricks. Unprecedented high contents of up to 70 wt % O-gibbsite nanoplatelets are tolerated in injection molding. As verified by focused ion beam-scanning electron microscopy (FIB-SEM), the resulting brick-and-mortar architectures contain aligned O-gibbsite as bricks and UHMWPE/high-density polyethylene (HDPE) shish-kebab structures as mortar. The resulting nacre-mimetic hydrocarbon/O-gibbsite composites exhibit substantially improved mechanical properties, as evidenced by high tensile strength of 200 MPa and a superior notched Izod impact strength (28 kJ/m2). In contrast to other nacre-mimetic composites, these superb mechanical properties are retained after immersing the composites in water for several days. As ?-Al(OH)3 splits off the water at elevated temperature, nacre-inspired hydrocarbon composites are flame retardant despite the high flammability of hydrocarbons. 72: Nanostructured pH-responsive polyelectrolyte amphiphilic polymer conetworks Ivan, Bela; Pasztor, Szabolcs; Fodor, Csaba; Haraszti, Marton; Kali, Gergely; Thomann, Yi; Thomann, Ralf; Mulhaupt, Rolf From Abstracts of Papers, 256th ACS National Meeting and Exposition, Boston, MA, United States, August 19-23, 2018 (2018), POLY-398. Abstract: Amphiphilic conetworks composed of covalently linked immiscible hydrophobic and hydrophilic polymer chains provide a variety of unique properties and functions. In this presentation, the unusual synthesis routes, structure-property relations and unprecedented pH-responsive behavior of amphiphilic conetworks consisting of hydrophilic polyelectrolyte chains, with monomer units of either acidic or basic characters, such as (meth)acrylic acid or vinyl imidazole, resp., cross-linked with polyisobutylene (PIB) or poly(tetrahydrofuran) chains will be reported. 71: Különleges nanoszerkezetû amfifil kotérháló alapú gélek és nanohibridjeik (Unique nanostructured amphiphilic polymer conetworks, their gels and nanohybrids) Béla Iván, Ákos Szabó, Attila Domján, Gábor Erdodi, Csaba Fodor, Márton Harasz, Gergely Kali, Péter Mezey, Zsófia Osváth, Szabolcs Pásztor, Tímea Stumphauser, Tamás Tóth, Bence Varga, Attila Bóta, András Wacha, Ralf Thomann, Yi Thomann, Rolf Muelhaupt Magyar Kémiai Folyóirat, 2018, 124, p.171-176 doi.org/10.24100/mkf.2018.04.171 70: A deep conical agarose microwell array for adhesion independent three-dimensional cell culture and dynamic volume measurement Andreas R. Thomsen, Christine Aldriana, Anja Heselich, Nicolas Melin, G. Rücker, Peter Bronsert, Yi Thomann, Marie Follo, Norbert Nanko, Anca-L. Grosu, Gabriele Niedermann, Paul G. Layer and Per G. Lund Lab on a Chip (2018), 18(1), 179-189. Abstract: Multicellular spheroids represent a well-established 3D model to study healthy and diseased cells in vitro. The use of conventional 3D cell culture platforms for the generation of multicellular spheroids is limited to cell types that easily self-assemble into spheroids because less adhesive cells fail to form stable aggregates. A high-precision micromolding technique developed in our lab. produces deep conical agarose microwell arrays that allow the cultivation of uniform multicellular aggregates, irresp. of the spheroid formation capacity of the cells. Such hydrogel arrays warrant a steady nutrient supply for several weeks, permit live volumetric measurements to monitor cell growth, enable immunohistochem. staining, fluorescence-based microscopy, and facilitate immediate harvesting of cell aggregates. This system also allows co-cultures of two distinct cell types either in direct cell-cell contact or at a distance as the hydrogel permits diffusion of sol. compds. Notably, we show that co-culture of a breast cancer cell line with bone marrow stromal cells enhances 3D growth of the cancer cells in this system. 69: Nanophasic morphologies as a function of the composition and molecular weight of the macromolecular cross-linker in poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks: bicontinuous domain structure in broad composition ranges Csaba Fodor, Gergely Kali, Ralf Thomann, Yi Thomann, Bela Ivan, Rolf Mulhaupt RSC Advances (2017), 7(12), 6827-6834 Abstract: Macroscopically homogeneous poly(N-vinylimidazole)-linked by-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) were investigated to reveal the effect of conetwork compn. in a broad compn. range between 25-91 wt% PTHF content and the mol. wt. of the components on phase sepn. and the formation of different morphol. features. No macroscopic phase sepn. was found in these conetworks with semicryst. PTHF phase, but the segregation of the various covalently connected phases occurs in the nanoscale. The nanophase sepd. APCNs possess compositionally asym. morphol. with spherical and elongated domains together with a bicontinuous (cocontinuous) domain structure having 7-19 nm av. domain sizes. The mol. wt. of the PTHFDMA cross-?linker, varying between 2170 and 10 030 g mol-1, also influences the size and distance between the phases. Moreover, morphol. dependent interactions with polar and non-?polar solvents, as well as amphiphilic swelling behavior were found. These nanostructured materials, due to their unique nanophasic morphol. and swelling properties possess significant importance and have numerous potential applications in various fields from medicine to material science and engineering. 68: Nanostructured Polyethylene Reactor Blends with Tailored Trimodal Molar Mass Distributions as Melt-Processable All-Polymer Composites Markus Stuerzel, Timo Hees, Markus Enders, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt Macromolecules (Washington, DC, United States) (2016), 49(21), 8048-8060. Abstract: Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymn. on three-site catalysts, supported on functionalized graphene (FG), enables nanophase sepn. during polymn. and melt processing, paralleled by PE self-?reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)?chromium trichloride (CrBIP), producing PE wax having high crystn. rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh mol. wt. PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-Bu cyclopentadienyl)zirconium (ZrCp), resp., producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-?chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a built-in processing aid and enables the incorporation of much higher UHMWPE contents (30 wt. %) than previously thought to be tolerable in injection molding. Whereas the incorporation of UHMWPE/PE wax blends improves stiffness and strength, the simultaneous FG dispersion accounts for substantially higher impact strength. 67: Multisite catalyst mediated polymer nanostructure formation and self-reinforced polyethylene reactor blends with improved toughness/stiffness balance Markus Stuerzel, Alexander Kurek, Timo Hees, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt Polymer (2016), 102, 112-118 Abstract: The design of supported two- and three-site catalysts for ethylene polymn. and tailoring nanophase-?sepd. polyethylene reactor blends represents the key to the development of advanced all-polyethylene nanocomposite materials exhibiting substantially improved performance and high resource-, eco- and energy efficiency. Two or three different single-site catalysts independently produce high d. polyethylene (HDPE), ultrahigh mol. wt. polyethylene (UHMWPE) and PE wax on the same catalyst support. Since this catalyst-?mediated nanophase sepn. prevents UHMWPE entanglement, typical for conventional homogeneous reactor blends, much higher UHMWPE content up to 30 wt% is incorporated in the presence of PE wax without impairing injection molding. During melt processing the shear-induced oriented UHMWPE crystn. affords shish-kebab-fiber-like nanostructures. This accounts for effective PE self-reinforcement paralleled by simultaneous improvement of stiffness, strength and toughness. Hence, this strategy holds great promise for converting commodity PE into high performance plastics and single component PE composites, entering the performance range currently claimed by glass fiber reinforced PE. 66: Poly(N-vinylimidazole)-l-poly(propylene glycol) amphiphilic conetworks and gels: molecularly forced blends of incompatible polymers with single glass transition temperatures of unusual dependence on the composition Csaba Fodor, Timea Stumphauser, Ralf Thomann, Yi Thomann, Bela Ivan Polymer Chemistry (2016), 7(34), 5375-5385 Abstract: A series of macroscopically homogeneous poly(N-vinylimidazole)-l-poly(propylene glycol) (PVIm-l-PPG) ("l" stands for "linked by") amphiphilic conetworks (APCNs) composed of otherwise incompatible polymers were successfully synthesized in a broad compn. range (34-88 wt% PPG) by free radical copolymn. of hydrophilic N-vinylimidazole (VIm) and hydrophobic poly(propylene glycol) dimethacrylate (PPGDMA) macromol. cross-linkers. Strikingly, while PVIm and PPGDMA homopolymers are immiscible and their blends have two distinct glass transition temps. (Tg), the PVIm-l-PPG conetworks possess only one Tg indicating the absence of considerable phase sepn. in the conetworks, which was also confirmed by AFM measurements. This is in sharp contrast to the two Tgs of APCNs reported so far in the literature, on the one hand. On the other hand, the Tg values do not follow known correlations between Tg and compn., like the Fox equation or additive rule, widely applied for compatible polymers. These results indicate a strong interpolymer interaction on the mol. level between the PVIm and PPG chains in these new APCNs resulting in single Tg. Thermogravimetric anal. (TGA) shows that degrdn. of the conetworks occurs at high temps. in two stages without sharp changes, but with a transition period in between. The DTG curves indicate that the components retain their chem. integrity to certain extent in these APCNs. The amphiphilic nature of the PVIm-l-PPG conetworks was confirmed by their compn. dependent swelling in both polar (water, ethanol) and nonpolar (THF) solvents, that is in spite of the lack of phase sepn., these new materials behave as either hydrogels or hydrophobic gels (organogels) depending on the swelling medium in a broad compn. range. 65: Graphene-Supported Dual-Site Catalysts for Preparing Self-Reinforcing Polyethylene Reactor Blends Containing UHMWPE Nanoplatelets and in Situ UHMWPE Shish-Kebab Nanofibers Markus Stürzel, Yi Thomann, Markus Enders, and Rolf Mülhaupt Macromolecules, 2014, Volume47, Issue15, Pages 4979-4986 Abstract: The catalytic ethylene polymerization on dual-site catalysts, supported on functionalized graphene, enables nanostructure formation in polyethylene reactor blends by in situ formation of uniformly dispersed ultrahigh molecular weight polyethylene (UHMWPE) nanoplatelets and in situ formed aligned UHMWPE shish-kebab nanofibers. For tailoring bimodal molar mass distributions, the quinolylsilylcyclopentadienylchromium(III) complex (Cr-1), producing UHMWPE with Mw > 3 x 106 g mol-1, is blended together with bisiminopyridine complexes of either chromium(III) (CrBIP), producing polyethylene (PE) wax (2 x 103 g mol-1), or iron(II) (FeBIP), producing PE with Mw = 2.0 x 105 g mol-1. Hence, the FeBIP/Cr-1 and CrBIP/Cr-1 molar ratios govern the PE/UHMWPE weight ratio without affecting the average molar mass of the individual PE fractions. In sharp contrast to conventional UHMWPE/PE reactor blends, the UHMWPE content is substantially increased up to 17 wt % without impairing melt processing. In the case of graphene-supported FeBIP/Cr-1, SEM and TEM analysis reveal that UHMWPE nanoplatelets are formed during polymerization. This is attributed to graphene-mediated mesoscopic shape replication. During injection molding, the UHMWPE nanoplatelets are transformed into aligned UHMWPE shish-kebab nanofibers, thus enabling efficient polyethylene matrix reinforcement. 64: Gas phase mineralized graphene as core/shell nanosheet supports for single-site olefin polymerization catalysts and in-situ formation of graphene/polyolefin nanocomposites Felix Kirschvink, Markus Stürzel, Yi Thomann, Rolf Mülhaupt Polymer (2014), 55(18), 4547-4550. Abstract: A versatile gas phase mineralization process affords nanosheets containing a functionalized graphene (FG) core and a thin silica shell. The number of cycles, exposing FG to sequenced tetrachlorosilane and water vapors, controls the silica content and the silica shell thickness. The resulting high surface area core/shell nanosheets, containing 22 to 34 wt.-% silica, are used to immobilize single-site catalysts. During polymerization, the FG/silica nanosheets are uniformly dispersed in ultrahigh molecular weight polyethylene. This catalytic polymerization filling process, exploiting the encapsulation of graphene in a silica shell, is of interest to prepare electrically insulating carbon/polyolefin composite materials with high thermal conductivity useful in lightweight engineering. 63: Improving Melt Flow of Polyoxymethylene ("High-Speed POM"): Additive Design, Melt Rheology, and In Situ Composition Gradient Formation Karlheinz Gamp, Yi Thomann, Christian Friedrich, André Hebel, Kirsten Markgraf, Hanno Hückstädt, Klaus Kurz and Rolf Mülhaupt Macromolecular Materials and Engineering (2014), 299(1), 51264. Abstract: Variation of isocyanurate substitution patterns and functionalities is the key to novel additives for "high-speed POM". In injection molding only 3wt% isocyanurate urethane (I3O) are sufficient for increasing the POM melt flow path by 60%. Such additives can reduce processing temperature by 40?K. Lubrication mechanisms and the role of in situ composition gradient formation, resulting from additive surface migration, are studied. 62: Novel Graphene UHMWPE Nanocomposites Prepared by Polymerization Filling Using Single-Site Catalysts Supported on Functionalized Graphene Nanosheet Dispersions Markus Stürzel, Fabian Kempe, Yi Thomann, Stefan Mark, Markus Enders, and Rolf Mülhaupt Macromolecules, (2012), 45(17), 6878-6887. Abstract: Novel families of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites, containing uniformly dispersed, functionalized graphene (FG) nanosheets, were prepared by means of the polymerization filling technique (PFT). Unparalleled by any other carbon and boehmite nanocomposites, FG/UHMWPE exhibited an unusual simultaneous improvement in stiffness, elongation at break, and effective nucleation of polyethylene crystallization at only 1 wt % FG content. FG nanosheets are ultrathin-with a thickness of only one carbon atom and lateral dimensions of several micrometers. Owing to the presence of surface hydroxyl groups on the FG, single FG/methylaluminoxane (MAO) nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of an MAO-activated chromium (Cr1) single-site catalyst on FG. In contrast to nanometer-scale carbon black (CB), multiwall carbon nanotubes (CNT), graphite, and nanoboehmite, which failed to form stable dispersions, FG/MAO/Cr1 afforded the highest catalyst activities and excellent morphological control. In polymerization filling, the integration of a nanoparticle dispersion into the polymerization process eliminated the need for special safety and handling precautions typically required by conventional compounding of nanoparticles with ultralow bulk densities. 61: Turning Teflon-coated magnetic stirring bars to catalyst systems with metal nanoparticle trace deposits - a caveat and a chance Christian Vollmer, Marcel Schröder, Yi Thomann, Ralf Thomann, Christoph Janiak Applied Catalysis A: General, 425-426, p.178-183, May 2012 Abstract: It could be an unintentional effect to deposit metal nanoparticles on a simple Teflon-coated magnetic stirring bar. Rhodium nanoparticles, as an example, were reproducibly deposited onto a standard, commercial Teflon-coated magnetic stirring bar by easy and rapid microwave-assisted decomposition of the metal carbonyl precursor Rh6(CO)16 in the ionic liquid 1-n-butyl-3-methyl-imidazolium-tetrafluoroborate. Such metal nanoparticle deposits are not easy to remove from the Teflon surface by simple washing procedures and present active catalysts which one is not necessarily aware of. Barely visible metal-nanoparticle deposits on a stirring bar can act as trace metal impurities in catalytic reactions. As a proof-of-principle the rhodium-nanoparticle deposits of 32 µg or less Rh metal on a 20 × 6 mm magnetic stirring bar were shown to catalyze the hydrogenation reaction of neat cyclohexene or benzene to cyclohexane with quantitative conversion. Rhodium-nanoparticle-coated stirring bars were easily handable, separable and re-usable catalyst system for the heterogeneous hydrogenation with quantitative conversion and very high turnover frequencies of up to 32800 mol cyclohexene × (mol Rh)-1 × h-1 under organic-solvent-free conditions. 60: Self-Healing Rubbers Based on NBR Blends with Hyperbranched Polyethylenimines Andreas C. Schüssele, Fritz Nübling, Yi Thomann, Oliver Carstensen, Georg Bauer, Thomas Speck, Rolf Mülhaupt Macromolecular Materials and Engineering, Volume 297, Issue 5, May 2012, Pages: 411-419 Abstract: Hyperbranched PEI and urea-functionalized PEI amphiphiles are employed as additives in NBR compounding. Polarity design governing phase separation, PEI migration and PEI-mediated self-healing of NBR is demonstrated. The compatibility of PEI and NBR decreases with increasing molecular weight of PEI and with decreasing degree of substitution. Microphase-separated NBR/PEI blends are prepared with varying PEI molecular architectures. Thermal self-healing of NBR/PEI is monitored by applying tests combining crack initiation with annealing under compression. All PEI additives show complete crack-healing upon annealing at 100°C for 12h. In contrast to neat NBR, the NBR/PEI-2 blend afforded a self-healing efficiency of 44% after cutting and re-joining by compression and annealing. 59: Comparison of bacterial adhesion and cellular proliferation on newly developed three-dimensional scaffolds manufactured by rapid prototyping technology A. Al-Ahmad, C. Schubert, C. Carvalho, Y. Thomann, A. Wittmer, M. Metzger, E. Hellwig, W. Swieszkowski, M. Wiedmann-Al-Ahmad Journal of Biomedical Materials Research, Part A (2011), 98(2), 303-311. Abstract: Scaffolds used in the field of tissue engineering should facilitate the adherence, spreading, and ingrowth of cells as well as prevent microbial adherence. For the first time, this study simultaneously deals with microbial and tissue cell adhesion to rapid prototyping-produced 3D-scaffolds. The cell growth of human osteosarcoma cells (CAL-72) over a time period of 3-11 days were examined on three scaffolds (PLGA, PLLA, PLLA-TCP) and compared to the adhesion of salivary microorganisms and representative germs of the oral flora (Porphyromonas gingivalis, Prevotella nigrescens, Candida albicans, Enterococcus faecalis, Streptococcus mutans, and Streptococcus sanguinis). Scanning electron microscopy (SEM), cell proliferation measurements, and determination of the colony forming units (CFU) were performed. The cell proliferation rates on PLLA and PLLA-TCP after 3, 7, and 11 days of cultivation were higher than on PLGA. On day 3 the proliferation rates on PLLA and PLLA-TCP, and on day 5 on PLLA-TCP, proved to be significantly higher compared to that of the control (culture plate). The strain which showed the most CFUs on all of the investigated scaffolds was P. gingivalis, followed by E. faecalis. No significant CFU differences were determined examining P. gingivalis among the biomaterials. In contrast, E. faecalis was significantly more adherent to PLGA and PLLA compared to PLLA-TCP. The lowest CFU values were seen with C. albicans and P. nigrescens. Salivary born aerobic and anaerobic microorganisms adhered significantly more to PLGA compared to PLLA-TCP. These results supported by SEM point out the high potential of PLLA-TCP in the field of tissue engineering. 58: The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices Weiwei Li, Yi Zhou, B. Viktor Andersson, L. Mattias Andersson, Yi Thomann, Clemens Veit, Kristofer Tvingstedt, Ruiping Qin, Zhishan Bo, Olle Inganäs, Uli Würfel and Fengling Zhang Organic Electronics, (2011), 12(9), 1544-1551 Abstract: How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year. 57: Protein yoctowell nanoarchitectures: assembly of donut shaped protein containers and nanofibres. Andreas Schreiber, Ekaterina Zaitseva, Yi Thomann,Ralf Thomann, Joern Dengjel, Ralf Hanselmann, Stefan M. Schiller Soft Matter (2011), 7(6), 2875-2878. Abstract: Proteins able to form "donut shaped" assemblies have been expressed in Escherichia coli and used for reversible in vitro assembly of cylindrical yoctowells (yoctolitre: 1 yL = 10^-24 L). Their assembly and disassembly were studied spectroscopically and fibers ranging from mol. to multibundle structures have been assembled. 56: Amphiphilic polymer conetworks as chiral separation membranes Jan Tobis, Lisa Boch, Yi Thomann and Jörg C. Tiller Journal of Membrane Science, Volume 372, Issues 1-2, 15 April 2011, Pages 219-227 Abstract: There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)-N-(1-hydroxy-butan-2-yl)acrylamide( (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n(heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases. 55: Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose Arno M. Bieser, Yi Thomann, Jörg C. Tiller Macromolecular Bioscience, 2011, 11, 111-121 Abstract: A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase. 54: Novel acrylic nanocomposites containing in-situ formed calcium phosphate/layered silicate hybrid nanoparticles for photochemical rapid prototyping, rapid tooling and rapid manufacturing processes Matthias Gurr, Yi Thomann, Michael Nedelcu, Rainer Kübler, Laszlo Könczöl, Rolf Mülhaupt Polymer (2010), 51(22), 5058-5070 Abstract: Novel acrylic nanocomposites containing calcium phosphate/layered silicate hybrid nanoparticles have been developed for use in photochemical Rapid Prototyping processes like Structural Light Modulation (SLM) and Stereolithography (SL). When tertiary alkyl amines, protonated with phosphoric acid, were added to an acrylic suspension of calcium bentonite, the cation exchange of Ca2+ rendered bentonite organophilic, caused swelling, intercalation and dispersion of silicate nanoplatelets in the monomer. The simultaneous precipitation of calcium phosphate onto the silicate nanoplatelets accounted for the in-situ formation of hybrid nanoparticles. The uniform dispersions of such hybrid nanoparticles afforded a high degree of shear thinning, reflecting the presence of anisotropic filler particles, and increased photosensitivity in SLM with respect to the unfilled resin. Young's modulus of green and postcured parts increased by 30% at a filler content of 15 wt.% with respect to that of the unfilled benchmark material. This enhanced stiffness was paralleled by 30% increased fracture toughness. As evidenced by fracture surface analysis using Environmental Electron Microscopy (ESEM) and optical microscopy, the improved energy dissipation at the crack tip correlated with roughness of the fracture surfaces, increasing with increasing filler content. Moreover, the examination of the volumetric polymerization shrinkage and the fabrication of H-shaped diagnostic specimens revealed that the nanocomposites were processed with high accuracy, increasing with increasing filler content. Nanocomposite morphologies, examined by means of Transmission Electron Microscopy (TEM), demonstrated that the large primary bentonite particles with average diameters >10 µm fragmented into much smaller particles with average diameters in the range of 1 µm. According to TEM and Wide Angle X-Ray Scattering (WAXS), such in-situ formed nanoparticles were composed of both stacks of organoclay nanoplatelets and also isolated nanoplatelets typical for fully exfoliated organoclays. 53: Synthesis and characterization of chiral and thermo responsive amphiphilic conetworks Jan Tobis, Yi Thomann, Jörg C. Tiller Polymer (2010), 51(1), 35-45 Abstract: Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (-)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks.

Veröffentlichungen - Dr. Yi Thomann 2010-2025

84: Abiotic Acyl Transfer Cascades Driven by Aminoacyl Phosphate Esters and Self-Assembly
Mahesh D Pol, Ralf Thomann, Yi Thomann, Charalampos G Pappas
J. Am. Chem. Soc. 2024, 146, 43, 29621-29629
doi.org/10.1021/jacs.4c10082

Abstract: Biochemical acyl transfer cascades, such as those initiated by the adenylation of carboxylic acids, are central to various biological processes, including protein synthesis and fatty acid metabolism. Designing cascade reactions in aqueous media remains challenging due to the need to control multiple, sequential reactions in a single pot and manage the stability of reactive intermediates. Herein, we developed abiotic cascades using aminoacyl phosphate esters, the synthetic counterparts of biological aminoacyl adenylates, to drive sequential chemical reactions and self-assembly in a single pot. We demonstrated that the structural elements of amino acid side chains (aromatic versus aliphatic) significantly influence the reactivity and half-lives of aminoacyl phosphate esters, ranging from hours to days. This behavior, in turn, affects the number of couplings we can achieve in the network and the self-assembly propensity of activated intermediate structures. The cascades are constructed using bifunctional peptide substrates featuring side chain nucleophiles. Specifically, aromatic amino acids facilitate the formation of transient thioesters, which preorganized into spherical aggregates and further couple into chimeric assemblies composed of esters and thioesters. In contrast, aliphatic amino acids, which lack the ability to form such structures, predominantly undergo hydrolysis, bypassing further transformations after thioester formation. Additionally, in mixtures containing multiple aminoacyl phosphate esters and peptide substrates, we achieved selective product formation by following a distinct pathway that favors subsequent reactions through reactivity changes and self-assembly. By coupling chemical reactions with molecules of varying reactivity time scales, we can drive multiple reaction clocks with distinct lifetimes and self-assembly dynamics, facilitating precise temporal and structural regulation.

83: Microstructure of selective laser melted 316L under non-equilibrium solidification conditions
EF Özel, D Pede, C Müller, Y Thomann, R Thomann, H Mozaffari-Jovein
Journal of Experimental and Theoretical Analyses 1 (2), 64-73, 2023
doi.org/10.3390/jeta1020005

Abstract: In this study, the microstructural properties of selective laser melted 316L stainless steel were investigated using optical, scanning and transmission electron microscopy as well as X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy. The results show a very fine microstructure with visible melt pool boundaries and austenite as the predominant phase. Extremely fine sub-grain structures can be found within the grains, consisting of colonies of round or elongated cellular structures depending on orientations. Due to the prevailing cooling and solidification conditions, micro-segregations occur, leading to enrichment of the sub-grain boundaries with alloying elements such as silicon, chromium, manganese and molybdenum. The presence of ferrite could be detected in this area using TEM analysis.

82: High-Resolution Patterning of Organic-Inorganic Photoresins for Tungsten and Tungsten Carbide Microstructures
Manuel Luitz, Diana Pellegrini, Miriam von Holst, Khaled Seteiz, Lukas Gröner, Mario Schleyer, Michael Daub, Andreas Warmbold, Yi Thomann, Ralf Thomann, Frederik Kotz-Helmer, Bastian E Rapp
Advanced Engineering Materials 25 (13), 2201927, 2023
doi.org/10.1002/adem.202201927

Abstract: Tungsten is an important material for high-temperature applications due to its high chemical and thermal stability. Its carbide, that is, tungsten carbide, is used in tool manufacturing because of its outstanding hardness and as a catalyst scaffold due to its morphology and large surface area. However, microstructuring, especially high-resolution 3D microstructuring of both materials, is a complex and challenging process which suffers from slow speeds and requires expensive specialized equipment. Traditional subtractive machining methods, for example, milling, are often not feasible because of the hardness and brittleness of the materials. Commonly, tungsten and tungsten carbide are manufactured by powder metallurgy. However, these methods are very limited in the complexity and resolution of the produced components. Herein, tungsten ion-containing organic-inorganic photoresins, which are patterned by two-photon lithography (TPL) at micrometer resolution, are introduced. The printed structures are converted to tungsten or tungsten carbide by thermal debinding and reduction of the precursor or carbothermal reduction reaction, respectively. Using TPL, complex 3D tungsten and tungsten carbide structures are prepared with a resolution down to 2 and 7??m, respectively. This new pathway of structuring tungsten and its carbide facilitates a broad range of applications from micromachining to metamaterials and catalysis.

81: µ-CT Untersuchungen an heimischen Holzarten
Yi Thomann, Ralf Thomann
Poster - Zenodo, Published April 4, 2022
doi.org/10.5281/zenodo.6414287

Abstract: µ-CT an Kiefer, Eiche, Linde, Zwetschgenholz, Robinie, Rotbuche, Platane

80: The mineralization of various 3d-printed pcl composites
Artem Egorov, Bianca Riedel, Johannes Vinke, Hagen Schmal, Ralf Thomann, Yi Thomann, Michael Seidenstuecker
J. Funct. Biomater. 2022, 13(4), 238
doi.org/10.3390/jfb13040238

Abstract: In this project, different calcification methods for collagen and collagen coatings were compared in terms of their applicability for 3D printing and production of collagen-coated scaffolds. For this purpose, scaffolds were printed from polycaprolactone PCL using the EnvisionTec 3D Bioplotter and then coated with collagen. Four different coating methods were then applied: hydroxyapatite (HA) powder directly in the collagen coating, incubation in 10× SBF, coating with alkaline phosphatase (ALP), and coating with poly-L-aspartic acid. The results were compared by ESEM, µCT, TEM, and EDX. HA directly in the collagen solution resulted in a pH change and thus an increase in viscosity, leading to clumping on the scaffolds. As a function of incubation time in 10× SBF as well as in ALP, HA layer thickness increased, while no coating on the collagen layer was apparently observed with poly-L-aspartic acid. Only ultrathin sections and TEM with SuperEDX detected nano crystalline HA in the collagen layer. Exclusively the incubation in poly-L-aspartic acid led to HA crystals within the collagen coating compared to all other methods where the HA layers formed in different forms only at the collagen layer.

79: Laser Ablation on Isostatic Graphite-A New Way to Create Exfoliated Graphite
Maria Isabel Sierra-Trillo, Ralf Thomann, Ingo Krossing, Ralf Hanselmann, Rolf Mülhaupt, Yi Thomann
Materials 15 (16), 5474, 2022
doi.org/10.3390/ma15165474

Abstract: In search of a new way to fabricate graphene-like materials, isostatic graphite targets were ablated using high peak power with a nanosecond-pulsed infrared laser. We conducted dry ablations in an argon atmosphere and liquid-phase ablations in the presence of a liquid medium (water or toluene). After the dry ablation, the SEM images of the target showed carbon in the form of a volcano-like grain structure, which seemed to be the result of liquid carbon ejected from the ablation center. No graphite exfoliation could be achieved using dry ablation. When using liquid phase ablation with water or toluene as a liquid medium, no traces of the formation of liquid carbon were found, but cleaner and deeper craters were observed. In particular, when using toluene as a liquid medium, typical graphite exfoliation was found. We believe that due to the extremely high pressure and high temperature induced by the laser pulses, toluene was able to intercalate into the graphite layers. Between the laser pulses, the intercalated toluene was able to flash evaporate and blow-up the graphite, which resulted in exfoliated graphite. Exfoliated graphite was found on the ablated graphite surface, as well as in the toluene medium. The ablation experiments with toluene undertaken in this study demonstrated an effective method of producing micrometer-sized graphene material. When using water as a liquid medium, no massive graphite exfoliation was observed. This meant that under the used laser conditions, toluene was a better intercalant for graphite exfoliation than water.

78: An Artificial SEI Layer Based on an Inorganic Coordination Polymer with Self-Healing Ability for Long-Lived Rechargeable Lithium-Metal Batteries
Witali Beichel, Julian Skrotzki, Petra Klose, Christian Njel, Burkhard Butschke, Stephan Burger, Lili Liu, Ralf Thomann, Yi Thomann, Daniel Biro, Simon Thiele, Ingo Krossing
Batteries + supercaps 5 (2), e202100347, 2022
doi.org/10.1002/batt.202100347

Abstract: Upon immersion of a lithium (Li) anode into a diluted 0.05 to 0.20 M dimethoxyethane-solution of the phosphoric acid derivative (CF3CH2O)2P(O)OH (HBFEP), an artificial solid electrolyte interphase (SEI) is generated on the Li-metal surface. Hence, HBFEP reacts on the surface to the corresponding Li salt (LiBFEP), which is a Li-ion conducting inorganic coordination polymer. This film exhibits - due to the reversibly breaking ionic bonds - self-healing ability upon cycling-induced volume expansion of Li. The presence of LiBFEP as the major component in the artificial SEI is proven by ATR-IR and XPS measurements. SEM characterization of HBFEP-treated Li samples reveals porous layers on top of the Li surface with at least 3 ?m thickness. Li?Li symmetrical cells with HBFEP-modified Li electrodes show a three- to almost fourfold cycle-lifetime increase at 0.1 mA cm?2 in a demanding model electrolyte that facilitates fast battery failure (1 M LiOTf in TEGDME). Hence, the LiBFEP-enriched layer apparently acts as a Li-ion conducting protection barrier between Li and the electrolyte, enhancing the rechargeability of Li electrodes.

77: Facile fabrication of micro-/nanostructured, superhydrophobic membranes with adjustable porosity by 3D printing
Fadoua Mayoussi, Egan H Doeven, Andrea Kick, Andreas Goralczyk, Yi Thomann, Patrick Risch, Rosanne M Guijt, Frederik Kotz, Dorothea Helmer, Bastian E Rapp
J. Mater. Chem. A, 2021, 9, 21379-21386
doi.org/10.1039/D1TA03352B

Abstract: Porous membranes with special wetting properties have attracted great interest due to their various functions and wide applications, including water filtration, selective oil/water separation and oil skimming. Special wetting properties such as superhydrophobicity can be achieved by controlling the surface chemistry as well as the surface topography of a substrate. Three-dimensional (3D) printing is a promising method for the fast and easy generation of various structures. The most common method for 3D printing of superhydrophobic materials is a two-step fabrication process: 3D printing of user-defined topographies, such as surface structures or bulk porosity, followed by a chemical post-processing with low-surface energy chemicals such as fluorinated silanes. Another common method is using a hydrophobic polymer ink to print intricate surface structures. However, the resolution of most common printers is not sufficient to produce nano-/microstructured textures, moreover, the resulting delicate surface micro- or nanostructures are very prone to abrasion. Herein, we report a simple approach for 3D printing of superhydrophobic micro-/nanoporous membranes in a single step, combining the required topography and chemistry. The bulk porosity of this material, which we term "Fluoropor", makes it insensitive to abrasion. To achieve this, a photocurable fluorinated resin is mixed with a porogen mixture and 3D printed using a stereolithography (SLA) printing process. This way, micro-/nanoporous membranes with superhydrophobic properties with static contact angles of 164° are fabricated. The pore size of the membranes can be adjusted from 30 nm to 300 nm by only changing the porogen ratio in the mixture. We show the applicability of the printed membranes for oil/water separation and the formation of Salvinia layers which are of great interest for drag reduction in maritime transportation and fouling prevention.

76: Analysis of the Growth of Laterally Aligned SnO2 Nanowires by Thermodynamic Considerations and Experiments
Jasmin-Clara Bürger, Sebastian Gutsch, Yi Thomann, Ralf Thomann, Bjoern Christian, Oliver Ambacher, Margit Zacharias
Cryst. Growth Des. 2021, 21, 1, 191-199
doi.org/10.1021/acs.cgd.0c00983

Abstract: Recently, we reported the experimental tuning of the growth of freestanding SnO2 nanowires to a laterally aligned nanowire growth mode. Here, we present thermodynamic considerations taking into account the previously reported influencing parameters determining the experiments, i.e., the total pressure, the Sn/O ratio at the sample sites, the nanowire diameter, and the substrate type. We will discuss process parameters which will prefer a laterally aligned growth mode. We show that a continuous gold film used as catalyst inhibits the laterally aligned growth. Only at the edges the lateral growth can proceed, whereas the area region is covered by freestanding wires. The reason for that will be explained in a model. Furthermore, the laterally aligned nanowire surface faceting is analyzed by means of transmission electron microscopy and atomic force microscopy and explained.

75: The Scissors Effect in Action: The Fox-Flory Relationship between the Glass Transition Temperature of Crosslinked Poly(Methyl Methacrylate) and Mc in Nanophase Separated Poly(Methyl Methacrylate)-l-Polyisobutylene Conetworks
Szabolcs Pásztor, Bálint Becsei, Györgyi Szarka, Yi Thomann, Ralf Thomann, Rolf Mühlhaupt, Béla Iván
Materials 2020, 13(21), 4822
doi.org/10.3390/ma13214822

Abstract: The glass transition temperature (Tg) is one of the most important properties of polymeric materials. In order to reveal whether the scissors effect, i.e., the Fox-Flory relationship between Tg and the average molecular weight between crosslinking points (Mc), reported only in one case for polymer conetworks so far, is more generally effective or valid only for a single case, a series of poly(methyl methacrylate)-l-polyisobutylene (PMMA-l-PIB) conetworks was prepared and investigated. Two Tgs were found for the conetworks by DSC. Fox-Flory type dependence between Tg and Mc of the PMMA component (Tg = Tg,? ? K/Mc) was observed. The K constants for the PMMA homopolymer and for the PMMA in the conetworks were the same in the margin of error. AFM images indicated disordered bicontinuous, mutually nanoconfined morphology with average domain sizes of 5-20 nm, but the correlation between Tg and domain sizes was not found. These new results indicate that the macrocrosslinkers act like molecular scissors (scissors effect), and the Tg of PMMA depend exclusively on the Mc in the conetworks. Consequently, these findings mean that the scissors effect is presumably a general phenomenon in nanophase-separated polymer conetworks, and this finding could be utilized in designing, processing, and applications of these novel materials.

74: Nanoconfined Crosslinked Poly(ionic liquid)s with Unprecedented Selective Swelling Properties Obtained by Alkylation in Nanophase-Separated Poly(1-vinylimidazole)-l-poly(tetrahydrofuran) Conetworks
Tímea Stumphauser, György Kasza, Attila Domján, András Wacha, Zoltán Varga, Yi Thomann, Ralf Thomann, Balázs Pásztói, Tobias M. Trötschler, Benjamin Kerscher, Rolf Mülhaupt and Béla Iván
Polymers 2020, 12(10), 2292
doi.org/10.3390/polym12102292

Abstract: Despite the great interest in nanoconfined materials nowadays, nanocompartmentalized poly(ionic liquid)s (PILs) have been rarely investigated so far. Herein, we report on the successful alkylation of poly(1-vinylimidazole) with methyl iodide in bicontinuous nanophasic poly(1-vinylimidazole)-l-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) to obtain nanoconfined methylated PVImMe-l-PTHF poly(ionic liquid) conetworks (PIL-CNs). A high extent of alkylation (~95%) was achieved via a simple alkylation process with MeI at room temperature. This does not destroy the bicontinuous nanophasic morphology as proved by SAXS and AFM, and PIL-CNs with 15-20 nm d-spacing and poly(3-methyl-1-vinylimidazolium iodide) PIL nanophases with average domain sizes of 8.2-8.4 nm are formed. Unexpectedly, while the swelling capacity of the PIL-CN dramatically increases in aprotic polar solvents, such as DMF, NMP, and DMSO, reaching higher than 1000% superabsorbent swelling degrees, the equilibrium swelling degrees decrease in even highly polar protic (hydrophilic) solvents, like water and methanol. An unprecedented Gaussian-type relationship was found between the ratios of the swelling degrees versus the polarity index, indicating increased swelling for the nanoconfined PVImMe-l-PTHF PIL-CNs in solvents with a polarity index between ~6 and 9.5. In addition to the nanoconfined structural features, the unique selective superabsorbent swelling behavior of the PIL-CNs can also be utilized in various application fields.

73: Melt-Processable Nacre-Mimetic Hydrocarbon Composites via Polymer 1D Nanostructure Formation
F. Zhong, R. Thomann, Y. Thomann, L. Burk, R. Mülhaupt
Macromolecules 2019, 52, 23, 9272-9279
doi.org/10.1021/acs.macromol.9b01184

Abstract: Nacre-mimicking layered organic/inorganic hybrid materials exhibiting ultrahigh stiffness and strength frequently require multistep processing that is restricted to polar and even water-soluble polymers. Herein, nacre-mimetic hydrocarbon composites were fabricated by single-step injection molding. The key intermediates are organophilic ultrathin ?-Al(OH)3 (O-gibbsite) single-crystal nanoplatelets and all-hydrocarbon composites (All-PE) containing aligned, extended-chain ultrahigh-molecular-weight polyethylene (UHMWPE) as one-dimensional (1D) nanostructures embedded in a polyethylene (PE) matrix. This formation of flow-induced UHMWPE 1D nanostructures mimics chitin nanofibers in nacre and drives the alignment of O-gibbsite nanoplatelets to assemble bricks. Unprecedented high contents of up to 70 wt % O-gibbsite nanoplatelets are tolerated in injection molding. As verified by focused ion beam-scanning electron microscopy (FIB-SEM), the resulting brick-and-mortar architectures contain aligned O-gibbsite as bricks and UHMWPE/high-density polyethylene (HDPE) shish-kebab structures as mortar. The resulting nacre-mimetic hydrocarbon/O-gibbsite composites exhibit substantially improved mechanical properties, as evidenced by high tensile strength of 200 MPa and a superior notched Izod impact strength (28 kJ/m2). In contrast to other nacre-mimetic composites, these superb mechanical properties are retained after immersing the composites in water for several days. As ?-Al(OH)3 splits off the water at elevated temperature, nacre-inspired hydrocarbon composites are flame retardant despite the high flammability of hydrocarbons.

72: Nanostructured pH-responsive polyelectrolyte amphiphilic polymer conetworks
Ivan, Bela; Pasztor, Szabolcs; Fodor, Csaba; Haraszti, Marton; Kali, Gergely; Thomann, Yi; Thomann, Ralf; Mulhaupt, Rolf
From Abstracts of Papers, 256th ACS National Meeting and Exposition, Boston, MA, United States, August 19-23, 2018 (2018), POLY-398.

Abstract: Amphiphilic conetworks composed of covalently linked immiscible hydrophobic and hydrophilic polymer chains provide a variety of unique properties and functions. In this presentation, the unusual synthesis routes, structure-property relations and unprecedented pH-responsive behavior of amphiphilic conetworks consisting of hydrophilic polyelectrolyte chains, with monomer units of either acidic or basic characters, such as (meth)acrylic acid or vinyl imidazole, resp., cross-linked with polyisobutylene (PIB) or poly(tetrahydrofuran) chains will be reported.

71: Különleges nanoszerkezetû amfifil kotérháló alapú gélek és nanohibridjeik
(Unique nanostructured amphiphilic polymer conetworks, their gels and nanohybrids)
Béla Iván, Ákos Szabó, Attila Domján, Gábor Erdodi, Csaba Fodor, Márton Harasz, Gergely Kali, Péter Mezey, Zsófia Osváth, Szabolcs Pásztor, Tímea Stumphauser, Tamás Tóth, Bence Varga, Attila Bóta, András Wacha, Ralf Thomann, Yi Thomann, Rolf Muelhaupt
Magyar Kémiai Folyóirat, 2018, 124, p.171-176

doi.org/10.24100/mkf.2018.04.171

70: A deep conical agarose microwell array for adhesion independent three-dimensional cell culture and dynamic volume measurement
Andreas R. Thomsen, Christine Aldriana, Anja Heselich, Nicolas Melin, G. Rücker, Peter Bronsert, Yi Thomann, Marie Follo, Norbert Nanko, Anca-L. Grosu, Gabriele Niedermann, Paul G. Layer and Per G. Lund
Lab on a Chip (2018), 18(1), 179-189.

Abstract: Multicellular spheroids represent a well-established 3D model to study healthy and diseased cells in vitro. The use of conventional 3D cell culture platforms for the generation of multicellular spheroids is limited to cell types that easily self-assemble into spheroids because less adhesive cells fail to form stable aggregates. A high-precision micromolding technique developed in our lab. produces deep conical agarose microwell arrays that allow the cultivation of uniform multicellular aggregates, irresp. of the spheroid formation capacity of the cells. Such hydrogel arrays warrant a steady nutrient supply for several weeks, permit live volumetric measurements to monitor cell growth, enable immunohistochem. staining, fluorescence-based microscopy, and facilitate immediate harvesting of cell aggregates. This system also allows co-cultures of two distinct cell types either in direct cell-cell contact or at a distance as the hydrogel permits diffusion of sol. compds. Notably, we show that co-culture of a breast cancer cell line with bone marrow stromal cells enhances 3D growth of the cancer cells in this system.

69: Nanophasic morphologies as a function of the composition and molecular weight of the macromolecular cross-linker in poly(N-vinylimidazole)-l-poly(tetrahydrofuran) amphiphilic conetworks: bicontinuous domain structure in broad composition ranges
Csaba Fodor, Gergely Kali, Ralf Thomann, Yi Thomann, Bela Ivan, Rolf Mulhaupt
RSC Advances (2017), 7(12), 6827-6834

Abstract: Macroscopically homogeneous poly(N-vinylimidazole)-linked by-poly(tetrahydrofuran) (PVIm-l-PTHF) amphiphilic conetworks (APCNs) were investigated to reveal the effect of conetwork compn. in a broad compn. range between 25-91 wt% PTHF content and the mol. wt. of the components on phase sepn. and the formation of different morphol. features. No macroscopic phase sepn. was found in these conetworks with semicryst. PTHF phase, but the segregation of the various covalently connected phases occurs in the nanoscale. The nanophase sepd. APCNs possess compositionally asym. morphol. with spherical and elongated domains together with a bicontinuous (cocontinuous) domain structure having 7-19 nm av. domain sizes. The mol. wt. of the PTHFDMA cross-?linker, varying between 2170 and 10 030 g mol-1, also influences the size and distance between the phases. Moreover, morphol. dependent interactions with polar and non-?polar solvents, as well as amphiphilic swelling behavior were found. These nanostructured materials, due to their unique nanophasic morphol. and swelling properties possess significant importance and have numerous potential applications in various fields from medicine to material science and engineering.

68: Nanostructured Polyethylene Reactor Blends with Tailored Trimodal Molar Mass Distributions as Melt-Processable All-Polymer Composites
Markus Stuerzel, Timo Hees, Markus Enders, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt
Macromolecules (Washington, DC, United States) (2016), 49(21), 8048-8060.

Abstract: Tailoring trimodal polyethylene (PE) molar mass distributions by means of ethylene polymn. on three-site catalysts, supported on functionalized graphene (FG), enables nanophase sepn. during polymn. and melt processing, paralleled by PE self-?reinforcement. Typically, FG/MAO-supported three-site catalysts combine bis(iminopyridyl)?chromium trichloride (CrBIP), producing PE wax having high crystn. rate, and quinolylcyclopentadienylchromium dichloride (CrQCp), forming in situ ultrahigh mol. wt. PE (UHMWPE) nanostructures, with bis(iminopyridyl)iron dichloride (FeBIP) or bis(tert-Bu cyclopentadienyl)zirconium (ZrCp), resp., producing HDPE with variable intermediate molar mass. During injection molding, the formation of shish-kebab fiber-like extended-?chain UHMWPE structures, as verified by SEM, AFM, and DSC, account for effective self-reinforcement. Only in the presence of high UHMWPE content, PE wax, usually an unwanted byproduct in HDPE synthesis, functions as a built-in processing aid and enables the incorporation of much higher UHMWPE contents (30 wt. %) than previously thought to be tolerable in injection molding. Whereas the incorporation of UHMWPE/PE wax blends improves stiffness and strength, the simultaneous FG dispersion accounts for substantially higher impact strength.

67: Multisite catalyst mediated polymer nanostructure formation and self-reinforced polyethylene reactor blends with improved toughness/stiffness balance
Markus Stuerzel, Alexander Kurek, Timo Hees, Yi Thomann, Hannes Blattmann, Rolf Muelhaupt
Polymer (2016), 102, 112-118

Abstract: The design of supported two- and three-site catalysts for ethylene polymn. and tailoring nanophase-?sepd. polyethylene reactor blends represents the key to the development of advanced all-polyethylene nanocomposite materials exhibiting substantially improved performance and high resource-, eco- and energy efficiency. Two or three different single-site catalysts independently produce high d. polyethylene (HDPE), ultrahigh mol. wt. polyethylene (UHMWPE) and PE wax on the same catalyst support. Since this catalyst-?mediated nanophase sepn. prevents UHMWPE entanglement, typical for conventional homogeneous reactor blends, much higher UHMWPE content up to 30 wt% is incorporated in the presence of PE wax without impairing injection molding. During melt processing the shear-induced oriented UHMWPE crystn. affords shish-kebab-fiber-like nanostructures. This accounts for effective PE self-reinforcement paralleled by simultaneous improvement of stiffness, strength and toughness. Hence, this strategy holds great promise for converting commodity PE into high performance plastics and single component PE composites, entering the performance range currently claimed by glass fiber reinforced PE.

66: Poly(N-vinylimidazole)-l-poly(propylene glycol) amphiphilic conetworks and gels: molecularly forced blends of incompatible polymers with single glass transition temperatures of unusual dependence on the composition
Csaba Fodor, Timea Stumphauser, Ralf Thomann, Yi Thomann, Bela Ivan
Polymer Chemistry (2016), 7(34), 5375-5385

Abstract: A series of macroscopically homogeneous poly(N-vinylimidazole)-l-poly(propylene glycol) (PVIm-l-PPG) ("l" stands for "linked by") amphiphilic conetworks (APCNs) composed of otherwise incompatible polymers were successfully synthesized in a broad compn. range (34-88 wt% PPG) by free radical copolymn. of hydrophilic N-vinylimidazole (VIm) and hydrophobic poly(propylene glycol) dimethacrylate (PPGDMA) macromol. cross-linkers. Strikingly, while PVIm and PPGDMA homopolymers are immiscible and their blends have two distinct glass transition temps. (Tg), the PVIm-l-PPG conetworks possess only one Tg indicating the absence of considerable phase sepn. in the conetworks, which was also confirmed by AFM measurements. This is in sharp contrast to the two Tgs of APCNs reported so far in the literature, on the one hand. On the other hand, the Tg values do not follow known correlations between Tg and compn., like the Fox equation or additive rule, widely applied for compatible polymers. These results indicate a strong interpolymer interaction on the mol. level between the PVIm and PPG chains in these new APCNs resulting in single Tg. Thermogravimetric anal. (TGA) shows that degrdn. of the conetworks occurs at high temps. in two stages without sharp changes, but with a transition period in between. The DTG curves indicate that the components retain their chem. integrity to certain extent in these APCNs. The amphiphilic nature of the PVIm-l-PPG conetworks was confirmed by their compn. dependent swelling in both polar (water, ethanol) and nonpolar (THF) solvents, that is in spite of the lack of phase sepn., these new materials behave as either hydrogels or hydrophobic gels (organogels) depending on the swelling medium in a broad compn. range.

65: Graphene-Supported Dual-Site Catalysts for Preparing Self-Reinforcing Polyethylene Reactor Blends Containing UHMWPE Nanoplatelets and in Situ UHMWPE Shish-Kebab Nanofibers
Markus Stürzel, Yi Thomann, Markus Enders, and Rolf Mülhaupt
Macromolecules, 2014, Volume47, Issue15, Pages 4979-4986

Abstract: The catalytic ethylene polymerization on dual-site catalysts, supported on functionalized graphene, enables nanostructure formation in polyethylene reactor blends by in situ formation of uniformly dispersed ultrahigh molecular weight polyethylene (UHMWPE) nanoplatelets and in situ formed aligned UHMWPE shish-kebab nanofibers. For tailoring bimodal molar mass distributions, the quinolylsilylcyclopentadienylchromium(III) complex (Cr-1), producing UHMWPE with Mw > 3 x 106 g mol-1, is blended together with bisiminopyridine complexes of either chromium(III) (CrBIP), producing polyethylene (PE) wax (2 x 103 g mol-1), or iron(II) (FeBIP), producing PE with Mw = 2.0 x 105 g mol-1. Hence, the FeBIP/Cr-1 and CrBIP/Cr-1 molar ratios govern the PE/UHMWPE weight ratio without affecting the average molar mass of the individual PE fractions. In sharp contrast to conventional UHMWPE/PE reactor blends, the UHMWPE content is substantially increased up to 17 wt % without impairing melt processing. In the case of graphene-supported FeBIP/Cr-1, SEM and TEM analysis reveal that UHMWPE nanoplatelets are formed during polymerization. This is attributed to graphene-mediated mesoscopic shape replication. During injection molding, the UHMWPE nanoplatelets are transformed into aligned UHMWPE shish-kebab nanofibers, thus enabling efficient polyethylene matrix reinforcement.

64: Gas phase mineralized graphene as core/shell nanosheet supports for single-site olefin polymerization catalysts and in-situ formation of graphene/polyolefin nanocomposites
Felix Kirschvink, Markus Stürzel, Yi Thomann, Rolf Mülhaupt
Polymer (2014), 55(18), 4547-4550.

Abstract: A versatile gas phase mineralization process affords nanosheets containing a functionalized graphene (FG) core and a thin silica shell. The number of cycles, exposing FG to sequenced tetrachlorosilane and water vapors, controls the silica content and the silica shell thickness. The resulting high surface area core/shell nanosheets, containing 22 to 34 wt.-% silica, are used to immobilize single-site catalysts. During polymerization, the FG/silica nanosheets are uniformly dispersed in ultrahigh molecular weight polyethylene. This catalytic polymerization filling process, exploiting the encapsulation of graphene in a silica shell, is of interest to prepare electrically insulating carbon/polyolefin composite materials with high thermal conductivity useful in lightweight engineering.

63: Improving Melt Flow of Polyoxymethylene ("High-Speed POM"): Additive Design, Melt Rheology, and In Situ Composition Gradient Formation
Karlheinz Gamp, Yi Thomann, Christian Friedrich, André Hebel, Kirsten Markgraf, Hanno Hückstädt, Klaus Kurz and Rolf Mülhaupt
Macromolecular Materials and Engineering (2014), 299(1), 51264.

Abstract: Variation of isocyanurate substitution patterns and functionalities is the key to novel additives for "high-speed POM". In injection molding only 3wt% isocyanurate urethane (I3O) are sufficient for increasing the POM melt flow path by 60%. Such additives can reduce processing temperature by 40?K. Lubrication mechanisms and the role of in situ composition gradient formation, resulting from additive surface migration, are studied.

62: Novel Graphene UHMWPE Nanocomposites Prepared by Polymerization Filling Using Single-Site Catalysts Supported on Functionalized Graphene Nanosheet Dispersions
Markus Stürzel, Fabian Kempe, Yi Thomann, Stefan Mark, Markus Enders, and Rolf Mülhaupt
Macromolecules, (2012), 45(17), 6878-6887.

Abstract: Novel families of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites, containing uniformly dispersed, functionalized graphene (FG) nanosheets, were prepared by means of the polymerization filling technique (PFT). Unparalleled by any other carbon and boehmite nanocomposites, FG/UHMWPE exhibited an unusual simultaneous improvement in stiffness, elongation at break, and effective nucleation of polyethylene crystallization at only 1 wt % FG content. FG nanosheets are ultrathin-with a thickness of only one carbon atom and lateral dimensions of several micrometers. Owing to the presence of surface hydroxyl groups on the FG, single FG/methylaluminoxane (MAO) nanosheets can be effectively dispersed in n-heptane, thus enabling immobilization of an MAO-activated chromium (Cr1) single-site catalyst on FG. In contrast to nanometer-scale carbon black (CB), multiwall carbon nanotubes (CNT), graphite, and nanoboehmite, which failed to form stable dispersions, FG/MAO/Cr1 afforded the highest catalyst activities and excellent morphological control. In polymerization filling, the integration of a nanoparticle dispersion into the polymerization process eliminated the need for special safety and handling precautions typically required by conventional compounding of nanoparticles with ultralow bulk densities.

61: Turning Teflon-coated magnetic stirring bars to catalyst systems with metal nanoparticle trace deposits - a caveat and a chance
Christian Vollmer, Marcel Schröder, Yi Thomann, Ralf Thomann, Christoph Janiak
Applied Catalysis A: General, 425-426, p.178-183, May 2012

Abstract: It could be an unintentional effect to deposit metal nanoparticles on a simple Teflon-coated magnetic stirring bar. Rhodium nanoparticles, as an example, were reproducibly deposited onto a standard, commercial Teflon-coated magnetic stirring bar by easy and rapid microwave-assisted decomposition of the metal carbonyl precursor Rh6(CO)16 in the ionic liquid 1-n-butyl-3-methyl-imidazolium-tetrafluoroborate. Such metal nanoparticle deposits are not easy to remove from the Teflon surface by simple washing procedures and present active catalysts which one is not necessarily aware of. Barely visible metal-nanoparticle deposits on a stirring bar can act as trace metal impurities in catalytic reactions. As a proof-of-principle the rhodium-nanoparticle deposits of 32 µg or less Rh metal on a 20 × 6 mm magnetic stirring bar were shown to catalyze the hydrogenation reaction of neat cyclohexene or benzene to cyclohexane with quantitative conversion. Rhodium-nanoparticle-coated stirring bars were easily handable, separable and re-usable catalyst system for the heterogeneous hydrogenation with quantitative conversion and very high turnover frequencies of up to 32800 mol cyclohexene × (mol Rh)-1 × h-1 under organic-solvent-free conditions.

60: Self-Healing Rubbers Based on NBR Blends with Hyperbranched Polyethylenimines
Andreas C. Schüssele, Fritz Nübling, Yi Thomann, Oliver Carstensen, Georg Bauer, Thomas Speck, Rolf Mülhaupt
Macromolecular Materials and Engineering, Volume 297, Issue 5, May 2012, Pages: 411-419

Abstract: Hyperbranched PEI and urea-functionalized PEI amphiphiles are employed as additives in NBR compounding. Polarity design governing phase separation, PEI migration and PEI-mediated self-healing of NBR is demonstrated. The compatibility of PEI and NBR decreases with increasing molecular weight of PEI and with decreasing degree of substitution. Microphase-separated NBR/PEI blends are prepared with varying PEI molecular architectures. Thermal self-healing of NBR/PEI is monitored by applying tests combining crack initiation with annealing under compression. All PEI additives show complete crack-healing upon annealing at 100°C for 12h. In contrast to neat NBR, the NBR/PEI-2 blend afforded a self-healing efficiency of 44% after cutting and re-joining by compression and annealing.

59: Comparison of bacterial adhesion and cellular proliferation on newly developed three-dimensional scaffolds manufactured by rapid prototyping technology
A. Al-Ahmad, C. Schubert, C. Carvalho, Y. Thomann, A. Wittmer, M. Metzger, E. Hellwig, W. Swieszkowski, M. Wiedmann-Al-Ahmad
Journal of Biomedical Materials Research, Part A (2011), 98(2), 303-311.

Abstract: Scaffolds used in the field of tissue engineering should facilitate the adherence, spreading, and ingrowth of cells as well as prevent microbial adherence. For the first time, this study simultaneously deals with microbial and tissue cell adhesion to rapid prototyping-produced 3D-scaffolds. The cell growth of human osteosarcoma cells (CAL-72) over a time period of 3-11 days were examined on three scaffolds (PLGA, PLLA, PLLA-TCP) and compared to the adhesion of salivary microorganisms and representative germs of the oral flora (Porphyromonas gingivalis, Prevotella nigrescens, Candida albicans, Enterococcus faecalis, Streptococcus mutans, and Streptococcus sanguinis). Scanning electron microscopy (SEM), cell proliferation measurements, and determination of the colony forming units (CFU) were performed. The cell proliferation rates on PLLA and PLLA-TCP after 3, 7, and 11 days of cultivation were higher than on PLGA. On day 3 the proliferation rates on PLLA and PLLA-TCP, and on day 5 on PLLA-TCP, proved to be significantly higher compared to that of the control (culture plate). The strain which showed the most CFUs on all of the investigated scaffolds was P. gingivalis, followed by E. faecalis. No significant CFU differences were determined examining P. gingivalis among the biomaterials. In contrast, E. faecalis was significantly more adherent to PLGA and PLLA compared to PLLA-TCP. The lowest CFU values were seen with C. albicans and P. nigrescens. Salivary born aerobic and anaerobic microorganisms adhered significantly more to PLGA compared to PLLA-TCP. These results supported by SEM point out the high potential of PLLA-TCP in the field of tissue engineering.

58: The Effect of additive on performance and shelf-stability of HSX-1/PCBM photovoltaic devices
Weiwei Li, Yi Zhou, B. Viktor Andersson, L. Mattias Andersson, Yi Thomann, Clemens Veit, Kristofer Tvingstedt, Ruiping Qin, Zhishan Bo, Olle Inganäs, Uli Würfel and Fengling Zhang
Organic Electronics, (2011), 12(9), 1544-1551

Abstract: How 1,8-diiodooctane (DIO) enhances performance of polymer solar cells based on polymer HXS-1 and fullerene [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) from 3.6% to 5.4% is scrutinized with several techniques by comparing devices or blend films spin-coated from dichlorobenzene (DCB) to those from DCB/DIO (97.5:2.5 v/v). Morphology of blend films is examined with atomic force microscopy (AFM), transmission electron microscopy (TEM) and electron tomography (3-D TEM), respectively. Charge generation and recombination is studied with photoluminescence, and charge transport with field effect transistors. The morphology with domain size in 10-20 nm and vertical elongated clusters formed in DIO system is supposed to facilitate charge transport and minimize charge carrier recombination, which are the main reasons for enhancing power conversion efficiency (PCE) from 3.6% (without DIO) to 5.4% (with DIO). Furthermore, a two year inspection shows no significant impact of DIO on the shelf-stability of the solar cells. No visible degradation in the second year indicates that the morphology of the active layers in the devices is relatively stable after initial relaxation in the first year.

57: Protein yoctowell nanoarchitectures: assembly of donut shaped protein containers and nanofibres.
Andreas Schreiber, Ekaterina Zaitseva, Yi Thomann,Ralf Thomann, Joern Dengjel, Ralf Hanselmann, Stefan M. Schiller
Soft Matter (2011), 7(6), 2875-2878.

Abstract: Proteins able to form "donut shaped" assemblies have been expressed in Escherichia coli and used for reversible in vitro assembly of cylindrical yoctowells (yoctolitre: 1 yL = 10^-24 L). Their assembly and disassembly were studied spectroscopically and fibers ranging from mol. to multibundle structures have been assembled.

56: Amphiphilic polymer conetworks as chiral separation membranes
Jan Tobis, Lisa Boch, Yi Thomann and Jörg C. Tiller
Journal of Membrane Science, Volume 372, Issues 1-2, 15 April 2011, Pages 219-227

Abstract: There is an urgent need for enantiopure chemicals, e.g., as basic compounds for pharmaceuticals. Although great progress has been made to obtain these compound using chiral catalysts, enzymes or even whole cells, it is often not possible or at least not economic to obtain enantiopure compounds. Thus enantioseparation is still required. Besides the elaborate and expensive chromatography and crystallization techniques, chiral membranes have been found to be effective in enantioseparation. Generally such membranes have to be developed specifically for a certain compound in a suited solvent. This is an elaborate development, because little is known about the complex transport process through a chiral membrane. In order to get better insights in the function of such membranes, we have designed a new class of chiral separating membranes that are applicable for nearly every solvent and therefore potentially many substrates. The conetworks are based on nanophasic, amphiphilic polymer conetworks (APCN) featuring a chiral phase of poly((R),(S)-N-(1-hydroxy-butan-2-yl)acrylamide( (P-(R),(S)-HBA) and a non-chiral polydimethylsiloxane (PDMS) phase. This APCN allows to directly exploring interactions between a chiral membrane and an enantiopure compound in dependence on a broad range of solvents varying from n(heptane to water by simply measuring the permeabilities of the compounds. Besides the numerous insights in the solvent-dependent interactions between membrane and five model substrates, we demonstrate that the APCNs are excellent chiral separation membranes. Further, it could be shown that the superior selectivity of these materials is based on the structure of their nanophases.

55: Contact-Active Antimicrobial and Potentially Self-Polishing Coatings Based on Cellulose
Arno M. Bieser, Yi Thomann, Jörg C. Tiller
Macromolecular Bioscience, 2011, 11, 111-121

Abstract: A contact-active antimicrobial coating is described that is only degraded in the presence of cellulase, which is an extracellular enzyme of numerous microbial strains. Antimicrobial DDA was grafted to a cellulose backbone via a polymeric spacer. The antimicrobial activity of the coatings, their biodegradability and their self-polishing potential were investigated. It was found that all coatings were antimicrobially active against Staphylococcus aureus. Coatings with high DS and long polymeric spacers degraded in water, while coatings with low DS and short spacers were not hydrolyzed even in the presence of cellulase. One coating was found to be selectively degradable by cellulase and recovered most of its antimicrobial activity after overloading and subsequent treatment with cellulase.

54: Novel acrylic nanocomposites containing in-situ formed calcium phosphate/layered silicate hybrid nanoparticles for photochemical rapid prototyping, rapid tooling and rapid manufacturing processes
Matthias Gurr, Yi Thomann, Michael Nedelcu, Rainer Kübler, Laszlo Könczöl, Rolf Mülhaupt
Polymer (2010), 51(22), 5058-5070

Abstract: Novel acrylic nanocomposites containing calcium phosphate/layered silicate hybrid nanoparticles have been developed for use in photochemical Rapid Prototyping processes like Structural Light Modulation (SLM) and Stereolithography (SL). When tertiary alkyl amines, protonated with phosphoric acid, were added to an acrylic suspension of calcium bentonite, the cation exchange of Ca2+ rendered bentonite organophilic, caused swelling, intercalation and dispersion of silicate nanoplatelets in the monomer. The simultaneous precipitation of calcium phosphate onto the silicate nanoplatelets accounted for the in-situ formation of hybrid nanoparticles. The uniform dispersions of such hybrid nanoparticles afforded a high degree of shear thinning, reflecting the presence of anisotropic filler particles, and increased photosensitivity in SLM with respect to the unfilled resin. Young's modulus of green and postcured parts increased by 30% at a filler content of 15 wt.% with respect to that of the unfilled benchmark material. This enhanced stiffness was paralleled by 30% increased fracture toughness. As evidenced by fracture surface analysis using Environmental Electron Microscopy (ESEM) and optical microscopy, the improved energy dissipation at the crack tip correlated with roughness of the fracture surfaces, increasing with increasing filler content. Moreover, the examination of the volumetric polymerization shrinkage and the fabrication of H-shaped diagnostic specimens revealed that the nanocomposites were processed with high accuracy, increasing with increasing filler content. Nanocomposite morphologies, examined by means of Transmission Electron Microscopy (TEM), demonstrated that the large primary bentonite particles with average diameters >10 µm fragmented into much smaller particles with average diameters in the range of 1 µm. According to TEM and Wide Angle X-Ray Scattering (WAXS), such in-situ formed nanoparticles were composed of both stacks of organoclay nanoplatelets and also isolated nanoplatelets typical for fully exfoliated organoclays.

53: Synthesis and characterization of chiral and thermo responsive amphiphilic conetworks
Jan Tobis, Yi Thomann, Jörg C. Tiller
Polymer (2010), 51(1), 35-45

Abstract: Amphiphilic polymer conetworks (APCN) combine the properties of different polymers on the nanoscale affording advanced materials with unique properties. Here, we present the first APCN with a chiral hydrophilic phase. The conetworks were prepared by copolymerizing the tailored chiral monomer (R)-N-(1-hydroxybutan-2-yl)acrylamide (R-HBA) with two different crosslinkers that consist of bitelechelic methacrylate-terminated poly(dimethylsiloxane) (PDMS) of a molecular weight of 1100 g/mol and 5620 g/mol, respectively. The resulting polymer conetworks P-R-HBA-l-PDMS exhibited both two different Tg values, indicating nanophase separation. However, the conetwork with PDMS1.1 did not show nanophases in the AFM and did not swell the phases separately in orthogonal solvents. On the other hand the materials with PDMS5.6 acted like a typical APCN. The APCN P-R-HBA-l-PDMS5.6 was found to be temperature sensitive in water, decreasing its degree of swelling linearly with increasing temperature. Additionally, the conetwork is increasing its degree of swelling in n-heptane in the region of the Tg of the P-R-HBA phase. The impact of the chiral polymer on the release of cinchona alkaloids was examined. For example, (-)-cinchonine diffuses four times faster off the P-R-HBA-l-PDMS networks than off the P-S-HBA-l-PDMS conetworks.