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Toughening Immiscible Polymer Blends The Role of Interface Crystallization Induced Compatibilization Explored Through Nanoscale Visualization
Get PDFThis study explores the novel approach of interface crystallization induced compatibilization ICIC via stereocomplexation as a promising method to improve the interfacial strength in thermodynamically immiscible polymers. Herein, two distinct reactive interfacial compatibilizers, poly styrene co glycidyl methacrylate graft poly l lactic acid SAL and poly styrene co glycidyl methacrylate graft poly d lactic acid SAD are synthesized via reactive melt blending in an integrated grafting and blending process. This approach is demonstrated to enhance the interfacial strength of immiscible polyvinylidene fluoride poly l lactic acid PVDF PLLA 50 50 blends via ICIC. IR nanoimaging indicates a cocontinuous morphology in the blends. The blend compatibilized with SAD exhibits a higher storage modulus, as unveiled by small amplitude oscillatory shear SAOS in the melt state at a temperature below the melting temperature of the stereocomplex SC crystals and by DMTA measurements in the solid state. This increase is attributed to the formation of a 200 300 nm thick rigid interfacial SC crystalline layer that is directly visible using AFM imaging and chemically characterized via IR nanospectroscopy. This ICIC also results in a significant toughening of the blend, with the elongation at break increasing more than 20 fold. Moreover, the fracture toughness factor obtained from single edge notch bending SENB tests is doubled with ICIC as compared to the uncompatibilized blend, indicating the strong crack resistance capability as a result of ICIC. This improvement is also evident in SEM images, where thinner and longer fibrillation is observed on the fractured surface in the presence of ICI
Tailoring perovskite crystallization and interfacial passivation in efficient, fully textured perovskite silicon tandem solar cells
Get PDFContext amp; scale Fully textured perovskite silicon tandem solar cells rely on the deposition of the perovskite absorber on textured silicon with a gt;1 amp; 956;m pyramid size, which represents the current standard in the industry. To bridge the gap between research and industry, these cells must demonstrate a high power output. Nevertheless, perovskite absorbers deposited on large pyramids often suffer from a high grain boundary defect density and poor interfacial passivation at the perovskite electron transport layer C60 junction. We tackle both loss mechanisms by introducing a multi functional additive urea , which simultaneously regulates the perovskite crystallization as well as passivates the perovskite C60 interface. Moreover, this strategy is employed at a low annealing temperature 100 C, different from the standardly used 150 C , thus enabling an effective lowering of the perovskite annealing s thermal budget. This approach is of high relevance for the industrialization of perovskite silicon tandem solar cells. Summary Fully textured perovskite silicon tandem solar cells are promising for future low cost photovoltaic deployment. However, the fill factor and open circuit voltage of these devices are currently limited by the high density of defects at grain boundaries and at interfaces with charge transport layers. To address this, we devise a strategy to simultaneously enhance perovskite crystallization and passivate the perovskite C60 interface. By incorporating urea CO NH2 2 as an additive in the solution step of the hybrid evaporation spin coating perovskite deposition method, the crystallization kinetics are accelerated, leading to the formation of the desired photoactive phase at room temperature. With that, perovskite films with large grain sizes gt;1 amp; 956;m and improved optoelectronic quality are formed at low annealing temperatures 100 C . Concurrently, remnant urea molecules are expelled at the perovskite surface, which locally displaces the C60 layer, thus reducing interfacial non radiative recombination losses. With this strategy, the resulting tandem solar cells achieve 30.0 power conversion efficienc
Accelerating wavepacket propagation with machine learning
Get PDFIn this work, we discuss the use of a recently introduced machine learning ML technique known as Fourier neural operators FNO as an efficient alternative to the traditional solution of the time dependent Schrödinger equation TDSE . FNOs are ML models which are employed in the approximated solution of partial differential equations. For a wavepacket propagating in an anharmonic potential and for a tunneling system, we show that the FNO approach can accurately and faithfully model wavepacket propagation via the density. Additionally, we demonstrate that FNOs can be a suitable replacement for traditional TDSE solvers in cases where the results of the quantum dynamical simulation are required repeatedly such as in the case of parameter optimization problems e.g., control . The speed up from the FNO method allows for its combination with the Markov chain Monte Carlo approach in applications that involve solving inverse problems such as optimal and coherent laser control of the outcome of dynamical processe
Two Isomeric Thienoacenes in Thin Films Unveiling the Influence of Molecular Structure and Intermolecular Packing on Electronic Properties
Get PDFIsomerism of molecular structures is often encountered in the field of organic semiconductors, but little is known about how it can impact electronic and charge transport properties in thin films. This study reveals the molecular orientation, electronic structure, and intermolecular interactions of two isomeric thienoacenes DN4T and isoDN4T in thin films, in relation to their charge transport properties. Utilizing scanning tunneling microscopy STM , angle resolved photoemission spectroscopy ARUPS , and near edge X ray absorption fine structure measurements NEXAFS , we systematically analyze the behavior of these isomers from submonolayer to multilayer coverage on highly ordered pyrolytic graphite HOPG as substrates. We find that at submonolayer coverage both DN4T and isoDN4T molecules predominantly adopt a nearly flat lying orientation on the surface, minimizing intermolecular interactions. The distinct emission features of the highest occupied molecular orbital HOMO level in ARUPS enables the determination of molecular reorganization energies. These are found to be in good agreement with theoretical predictions, suggesting superior charge transport in DN4T compared to isoDN4T. Notably, thickness dependent photoemission measurements reveal a significant splitting approximately 450 meV of the HOMO level of isoDN4T, attributed to polarizationinduced effects rather than wave function overlap, indicating a nuanced interplay between molecular packing and electronic properties. Our results underscore the importance of molecular packing and substrate interactions in determining the electronic structure and transport properties of organic semiconductor thin films. Substrate induced polymorphism and the crucial role of polarization induced effects influencing charge transport are highlighted. These insights are pivotal for future engineering of molecular and thin film structures, aiming to enhance the performance of organic semiconductor based device
Precise control of TiO2 overlayer on hematite nanorod arrays by ALD for the photoelectrochemical water splitting
Get PDFThe short lifetime of electron hole pairs and high electron hole recombination rate at surface states significantly limit the practical applications of hematite a Fe2O3 photoanodes in photoelectrochemical PEC water splitting. Surface modification with a TiO2 overlayer has been demonstrated to be an efficient way to improve the PEC performance. However, a fine control of the TiO2 overlayer and a deep understanding of the impact of the TiO2 overlayer with variable thickness on the PEC performance, to the best of our knowledge, has yet to be done. Here, a conformal ultrathin TiO2 overlayer is successfully deposited on hydrothermal grown one dimensional hematite nanorod arrays by atomic layer deposition. The morphology and thickness of the TiO2 overlayer can be precisely controlled. The effect of the thickness of the TiO2 overlayer on the overall water splitting efficiency of hematite photoanodes under visible and UV light has been systematically investigated. The charge excitation and transfer mechanism at the semiconductor electrolyte interface has also been studie
Advancements and Challenges in the Synthesis of Oxymethylene Ethers OMEs as Sustainable Transportation Fuels
Get PDFThe urgent need for sustainable alternatives to fossil fuels in the transportation sector is driving research into novel energy carriers that can meet the high energy density requirements of heavy duty vehicles without exacerbating the climate change. This concept article examines the synthesis, mechanisms, and challenges associated with oxymethylene ethers OMEs , a promising class of synthetic fuels potentially derived from carbon dioxide and hydrogen. We highlight the importance of OMEs in the transition towards non fossil energy sources due to their compatibility with the existing Diesel infrastructure and their cleaner combustion profile. The synthesis mechanisms, including the Schulz Flory distribution and its implications for OME chain length specificity, and the role of various catalysts and starting materials are discussed in depth. Despite advancements in the field, significant challenges remain, such as overcoming the Schulz Flory distribution, efficiently managing water as an undesirable byproduct, and improving the overall energy efficiency of the OME synthesis. Addressing these challenges is crucial for OMEs to become a viable alternative fuel, contributing to the reduction of greenhouse gas emissions and the transition to a sustainable energy future in the transportation sector. This concept reviews the recent advancements in the field of oxymethylene ether OME production. We discuss mechanistic details as well as synthesis conditions examined in the last decade. We identified the Schulz Flory product distribution, the energy efficiency, the influence of water as well as the production of suitable starting materials as the main challenges to establishing a large scale OME productio
Evaluation of in situ thermal stability assessment for flow batteries and deeper investigation of the ferrocene co polymer
Get PDFThe stability of reported organic materials for redox flow batteries RFB continues to improve. Consequently, the relevance of analytical techniques to assess degradation rates also grows. To contribute to the development of in operando thermal stability assessment techniques, we evaluated the commonly reported heating setups using the ferrocene based FPMAm co METAC polymer PFc in a Zn based hybrid RFB with a size exclusion membrane. In the first stage, the conditions for RFB cycling were selected and evaluated. The amperometric SOC measurement technique revealed oxygen intolerance of the PFc. While no polymer cross over was detected, cross over of its hydrolysis products occurred and facilitated the capacity fade. Adjustment of membrane pore size and electrolyte composition helped to mitigate the hydrolyzed products cross over. In the second stage, different heating setups for the thermal stability evaluation of PFc were compared. Eventually, a thermostatic setup established the desired temperature most accurately and homogeneously, while the popular oil sand bath setup exhibited a deviation of 22 degrees C down from the expected 60 degrees C. The PFc stability was further evaluated from ambient conditions 28 degrees C to 60 degrees C. At temperatures above 50 degrees C a facilitated capacity fade was observed. The volumetrically unbalanced, compositionally symmetric flow cell cycling has unraveled that the degradation was caused by catholyte self reduction and following half cell imbalances. A mechanism involving the ferrocene complex decomposition is proposed as the origin of the catholyte self reduction. Finally, the properties and thermal stability of the PFc material as well as the reliability of the studied heating setups are discusse
Solution Behavior of Glyco Copoly l Glutamic Acid s in Dilute Saline Solution
Get PDFA small series of copoly amp; 945;,l glutamic acid dl allylglycine s with the same chain length and allylglycine content amp; 8764;10 mol but different spatial distribution of allylglycine units was synthesized and subsequently glycosylated via thiol ene chemistry. Dilute aqueous copolypeptide solutions 0.1 wt , physiological saline were analyzed by circular dichroism spectroscopy, dynamic light scattering, and cryogenic transmission electron microscopy. The copolypeptides adopted a random coil or amp; 945; helix conformation, depending on solution pH, and the glycosylated residues either distorted or enhanced the folding into an amp; 945; helix depending on their location and spatial distribution along the chain. However, regardless of their secondary structure and degree of charging, all partially glycosylated copolypeptides self assembled into 3D spherical structures, supposedly driven by a hydrophilic effect promoting microphase separation into glucose rich and glutamate rich domain