A Periodic System of Supramolecular Elements Schmidt, Hans‐Werner; Würthner, Frank
Angewandte Chemie International Edition,
June 2, 2020, Letnik:
59, Številka:
23
Journal Article
Recenzirano
Chemistry “beyond the molecule” is based on weak, noncovalent, and reversible interactions. As a consequence of these bonds being weak, structural organization by folding and self‐assembly can only ...be fully exploited with larger molecules that can provide multiple binding sites. Such “supramolecules” can now be synthesized and their folding into desired conformations predicted. A new level of chemistry can now be realized through the creation of non‐natural entities composed of molecular building blocks with defined secondary structures. Herein we define these building blocks as “supramolecular elements”. We anticipate that further research on such large molecules will reveal construction principles dictated by recurring motifs that govern structure formation through folding and self‐assembly. These principles are comparable to the organization of atoms in the Periodic Table of Chemical Elements and may lead to the establishment of a Periodic System of Supramolecular Elements.
All systems go: Increased research on large molecules will reveal construction principles dictated by recurring motifs that govern structure formation through folding and self‐assembly. These principles are comparable to the organization of atoms in the Periodic Table of Chemical Elements and could lead to the establishment of a Periodic System of Supramolecular Elements.
Combining the unique corona structure of worm‐like patchy micelles immobilized on a polymer fiber with the molecular self‐assembly of 1,3,5‐benzenetricarboxamides (BTAs) leads to hierarchical ...superstructures with a fir‐tree‐like morphology. For this purpose, worm‐like patchy micelles bearing pendant, functional tertiary amino groups in one of the corona patches were prepared by crystallization‐driven self‐assembly and immobilized on a supporting polystyrene fiber by coaxial electrospinning. The obtained patchy fibers were then immersed in an aqueous solution of a tertiary amino‐functionalized BTA to induce patch‐mediated molecular self‐assembly to well‐defined fir‐tree‐like superstructures upon solvent evaporation. Interestingly, defined superstructures are obtained only if the pendant functional groups in the surface patches match with the peripheral substituents of the BTA, which is attributed to a local increase in BTA concentration at the polymer fibers’ surface.
Hierarchical fir‐tree‐like superstructures are accessible by utilizing the unique corona structure of patchy worm‐like micelles immobilized on electrospun polymer fibers and the molecular self‐assembly of a 1,3,5‐benzenetricarboxamide. The used combination of crystallization‐driven and molecular self‐assembly concepts can give access to a large variety of fibrillar superstructures with potential applications in filtration or catalysis.
Polymer fibers play an important role in nature and technical systems. Fiber morphologies with off‐standing branches, as found in nature, e.g. in penguin downy feathers, provide unique properties but ...are unknown for man‐made polymer fiber systems. We discovered that it is possible to initiate seeded growth from trisamide seeded polystyrene fibers, prepared by core‐shell electrospinning, to form off‐standing supramolecular trisamide branches similar to penguin downy feathers but in polymer nonwovens and in nanoscale. Resulting mesostructured nonwovens show unique properties. For example, air filtration efficiency of 99.8% for the filtration of 0.3 µm aerosol particles, being significantly higher compared to neat electrospun polystyrene nonwovens as bench‐mark, showing only an efficiency of about 52.6%. Most remarkably, the pressure drop observed in filtration tests and thus, the energy consumption during filtration, did not increase up to a certain content of off‐standing supramolecular fibrils. This is a unique behavior, as higher filtration capabilities are typically connected to higher energy consumptions and pressure drops. Hence, branching electrospun fibers with supramolecular fibrils paves the way to new mesostructured nonwovens with unique morphologies, property profiles and applications in filtration, catalysis, and energy storage/harvesting, exploiting nature's concepts.
Air pollution is a major burden for 21st century human society. Usually, there is a congruence of filtration efficiency and energy needed for filtration. This issue is herein resolved by applying hierarchically mesostructured nonwovens.
Wie kann die Integration von Geflüchteten in die Arbeitswelt gelingen? Werner Schmidt beschäftigt sich ausführlich mit dieser vielgestaltigen Frage und gibt durch zahlreiche Interviews mit ...betrieblichen Akteuren, Beschäftigten und Geflüchteten direkte Einblicke in alltägliche Chancen und Konfliktfelder. Dabei wird deutlich, dass die gegenwärtigen Bedingungen anders, aber keineswegs schlechter sind als bei der ersten »Gastarbeiter«-Generation. Größtes Problem ist heute jedoch das Eindringen rechtspopulistischer Diskurse. Die alltägliche Zusammenarbeit und die Anwendung gleicher Regeln für alle sind dagegen nützliche Mittel und sorgen für die Entwicklung von Kollegialität und Respekt unter Beschäftigten unterschiedlicher Herkunft.
A miniature small‐scale material processing and testing approach is developed as a screening method to evaluate polymer materials for fused deposition modeling (FDM). This method is suitable for a ...small material input of less than 10 g using a mini compounder in combination with an injection molding machine to manufacture short rods usable as FDM feedstock material. Compared with conventional continuous filament extrusion, where the amount of raw material required is around 1–5 kg, time and material consumption are both significantly reduced for the investigation of FDM filament materials or formulations. In order to demonstrate this method, three different polypropylene grades are processed into rods and compared to commercially available continuous filaments. In addition to warp deformation, interlayer bonding properties are also measured on test specimens punched out of FDM‐printed square tubes. The presented rod preparation and square tube printing offer fast and efficient material screening and optimization for new FDM material development.
Small‐scale material screening for fused deposition modeling (FDM) 3D printing by using injection molded short rods allows FDM printing in the same way as feeding continuous FDM filaments. By applying this method, material, time, and cost are minimized for the screening and investigation of FDM materials in the early development stage.
Melt electrowriting (MEW), an additive manufacturing process, is established using polycaprolactone as the benchmark material. In this study, a thermoplastic elastomer, namely, poly(urea‐siloxane), ...is synthesized and characterized to identify how different classes of polymers are compatible with MEW. This polyaddition polymer has reversible hydrogen bonding from the melt upon heating/cooling and highly resolved structures are achieved by MEW. The influence of applied voltage, temperature, and feeding pressure on printing outcomes behavior is optimized. Balancing these parameters, highly uniform and smooth‐surfaced fibers with diameters ranging from 10 to 20 µm result. The quality of the 3D MEW scaffolds is excellent, with very accurate fiber stacking capacity—up to 50 layers with minimal defects and good fiber fusion between the layers. There is also minimal fiber sagging between the crossover points, which is a characteristic of thicker MEW scaffolds previously reported with other polymers. In summary, poly(urea‐siloxane) demonstrates outstanding compatibility with the MEW process and represents a class of polymer—thermoplastic elastomers—that are, until now, untested with this approach.
A poly(urea‐siloxane) is synthesized, characterized, and melt‐electrowritten into well‐defined structures, with fibers ranging from 10 to 20 µm in diameter. The different macromolecular structures in the molten and solid phase of this thermoplastic elastomer are compatible with this additive manufacturing technology.
Information Systems Applications (incl.Internet); Business Information Systems; Computer Appl. in Administrative Data Processing; Management of Computing and Information Systems
High‐density polyethylene (HDPE) is one of the most widely used semi‐crystalline polyolefin thermoplastics. However, 3D printing with this material remains rare because of massive shrinkage and poor ...adhesion to common 3D printing build surfaces. In this study, shrinkage and warping were overcome by blending in short fibers of yellow birch at 10–30 wt% along with a coupling agent. Square tubes were printed to measure deformation and mechanical properties of this composite material. Deformation was reduced by 80% in material containing 30 wt% wood compared to neat HDPE. Young's modulus increased respectively by 25%, 30%, and 35% as the filler content increased to 10, 20, and 30 wt%. This is the first known successful 3D printing with wood‐fiber HDPE composite.
In nature, animals such as chameleons are well‐known for the complex color patterns of their skin and the ability to adapt and change the color by manipulating sophisticated photonic crystal systems. ...Artificial gradient photonic materials are inspired by these color patterns. A concept for the preparation of such materials and their function as tunable mechanochromic materials is presented in this work. The system consists of a 1D polymer photonic crystal on a centimeter scale on top of an elastic poly(dimethylsiloxane) substrate with a gradient in stiffness. In the unstrained state, this system reveals a uniform red reflectance over the entire sample. Upon deformation, a gradient in local strain of the substrate is formed and transferred to the photonic crystal. Depending on the magnitude of this local strain, the thickness of the photonic crystal decreases continuously, resulting in a position‐dependent blue shift of the reflectance peak and hence the color in a rainbow‐like fashion. Using more sophisticated hard‐soft‐hard‐soft‐hard gradient elastomers enables the realization of stripe‐like reflectance patterns. Thus, this approach allows for the tunable formation of reflectance gradients and complex reflectance patterns. Envisioned applications are in the field of mechanochromic sensors, telemedicine, smart materials, and metamaterials.
Gradient photonic materials consisting of a 1D polymer photonic crystal attached to an elastomer with a defined gradient in stiffness are able to change their color upon strain. Tuning the stiffness and the architecture of the gradient elastomer allows the formation of tailored reflectance patterns.
A novel nanoimprint lithography technique based on the photofluidization effect of azobenzene materials is presented. The tunable process allows for imprinting under ambient conditions without ...crosslinking reactions, so that shrinkage of the resist is avoided. Patterning of surfaces in the regime from micrometers down to 100 nm is demonstrated.
PDF
