Steffen Reich, Matthias Burgard, Markus Langner, Shaohua Jiang, Xueqin Wang, Seema Agarwal, Bin Ding, Jianyong Yu & Andreas Greiner
npj Flexible Electronics (2018) 2:5 ; doi:10.1038/s41528-017-0018-5.
Bendable and breathable polymer nanofibre nonwovens with metal-like electrical conductivity are required for lightweight electrodes and electric shielding design with applications in batteries, functional textiles, sensors, cars, aerospace, constructions, mobile phones, and medical devices. Metal-like conductivity in polymer nonwovens has not been achieved till now due to the limitation of the existing processing techniques. We show here, the metal-like electrical conductivity of 750,000 S/m in polyacrylonitrile (PAN), poly(ε-caprolactone) (PCL) nonwoven using very low content of silver nanowires (AgNW; 3.35 vol%). The key to the high conductivity was the homogenous distribution of AgNW in nonwoven made by wet-laid process using short electrospun fibre and AgNW dispersion. Above a threshold of 0.36 vol% AgNW, the conductivity of the nonwoven increased by seven orders of magnitude, which we attribute to the onset of percolation of the AgNW. Our nonwoven-AgNW composites show fast heating and cooling within a few seconds at a voltage of 1.1 V, which is in the range of portable devices. These composites are also breathable and bendable. The electrical conductivity was independent of the bending angle of the composite, which is important for applications mentioned above and would help other scientists to design new conductive materials in the future.
S. Jiang, G. Duan, U. Kuhn, M. Mörl, V. Altstädt, A. L. Yarin, A. Greiner
Angew.Chem. Int.Ed. 2017, 56,3285 –3288.
Ultralight cellular sponges offer a unique set of properties. We show here that solvent uptake by these sponges results in new gel-like materials, which we term spongy gels. The appearance of the spongy gels is very similar to classic organogels. Usually, organogels are formed by a bottom-up process. In contrast, the spongy gels are formed by a top-down approach that offers numerous advantages for the design of their properties, reproducibility, and stability. The sponges themselves represent the scaffold of a gel that could be filled with a solvent, and thereby form a mechanically stable gel-like material. The spongy gels are independent of a time-consuming or otherwise demanding in situ scaffold formation. As solvent evaporation from gels is a concern for various applications, we also studied solvent evaporation of wetting and non-wetting liquids dispersed in the sponge.
O.Hauenstein, Md. M.Rahman, M.Elsayed, R. Krause-Rehberg, S.Agarwal, V. Abetz and A. Greiner Adv. Mater. Technol. 2017, 1700026.
The biobased poly(limonene carbonate) (PLimC) synthesized by catalytic copolymerization of trans-limonene oxide and CO2 unifies sustainability, carbon capture and utilization of CO2 in one material. Films of PLimC show surprisingly high gas permeation and good selectivity. Additionally, it is not only very permeable to gases, but also to light, while simultaneously being a good heat insulator and mechanically strong, representing a novel type of material that is defined here as “breathing glass.” Hence, this study investigates the gas permeation and the selectivity in detail. The selectivity of PLimC for CO2 can be understood by its high fractional free volume, which is determined by positron annihilation lifetime spectroscopy supported by simulations. The CO2 permeability of PLimC at 30 °C is 68 barrer, while the CO2/N2 selectivity is ≈19, which places PLimC in a promising position in the Robeson plot and makes it unique due to its excellent transparency and processability under ambient conditions. Based on the high permeability of PLimC to gases and light, this study discusses here a completely new potential application of light transparent, gas-permeable polymer films as “breathing glass.”
Judith Schöbel, Matthias Burgard, Christian Hils, Dr. Roland Dersch, Dr. Martin Dulle, Kirsten Volk, Prof. Dr. Matthias Karg, Prof. Dr. Andreas Greiner, Dr. Holger Schmalz
Angew. Chem. Int. Ed. 2017, 56, 405-408.
Heterogeneous catalysis with supported nanoparticles (NPs) is a highly active field of research. However, the efficient stabilization of NPs without deteriorating their catalytic activity is challenging. By combining top-down (coaxial electrospinning) and bottom-up (crystallization-driven self-assembly) approaches, we prepared patchy nonwovens with functional, nanometer-sized patches on the surface. These patches can selectively bind and efficiently stabilize gold nanoparticles (AuNPs). The use of these AuNP-loaded patchy nonwovens in the alcoholysis of dimethylphenylsilane led to full conversion under comparably mild conditions and in short reaction times. The absence of gold leaching or a slowing down of the reaction even after ten subsequent cycles manifests the excellent reusability of this catalyst system. The flexibility of the presented approach allows for easy transfer to other nonwoven supports and catalytically active NPs, which promises broad applicability.
Li Liu, Ali Ghaemi, Stephan Gekle, Seema Agarwal
Advanced Materials, 2016, 28 (44), 9792-9796.
The work provides a rare example of a one-component dual actuator with irreversible change in shape by rolling on contact with water and reversible size change on changing the temperature. The actuator has a bilayer structure with aligned and randomly oriented fibers of poly (N-isopropyl acrylamide). A combination of anisotropic E modulus and temperature dependent swelling/shrinkage provides the dual actuation.
Oliver Hauenstein, Seema Agarwal, Andreas Greiner
Nature Communications 2016, 7, Article numer: 11862.
Completely bio-based poly(limonene carbonate) is a thermoplastic polymer, which can be synthesized by copolymerization of limonene oxide (derived from limonene, which is found in orange peel) and CO2. Poly(limonene carbonate) has one double bond per repeating unit that can be exploited for further chemical modifications.
Ziyin Fan, Xuelian Chen, Melissa Köhn Serrano, Holger Schmalz, Sabine Rosenfeldt,
Stephan Förster, Seema Agarwal und Andreas Greiner Angew. Chem. 2015, 127, 14747 –14752.
Eine neue, Templat-gestützte Synthese monodisperser Nanopartikel stellt keine Anforderungen an die Selbstorganisation und ist hoch reproduzierbar. Hierzu werden maßgeschneiderte Polymerkäfige für die Synthese von Nanopartikeln verwendet, die aus vernetzten Makromolekülen mit Thiolendgruppen bestehen. Goldnanopartikel (AuNPs) wurden in verschiedenen Verhältnissen von Polymerkäfig zu Gold in situ in den Polymerkäfigen synthetisiert. Die Polymerkäfige zeichneten sich dabei durch eine definierte Beladungskapazität aus, mit exzellenter Kontrolle über Form und Größe. Dagegen zeigten Kontrollversuche mit linearen Diblockcopolymeren einen linearen Anstieg der Partikelgrößen mit steigendem Goldanteil. Das unterschiedliche Wachstumsverhalten der AuNPs wird durch die Vernetzungsgrad-abhängige Flexibilität der Polymerketten erklärt. Des Weiteren wird die Polymerkäfig-gesteuerte In-situ-Synthese auf Silber- (AgNPs), Palladium- (PdNPs) und Platinnanopartikel (PtNPs) übertragen.
Li Liu, Shaohua Jiang, Yue Sun, and Seema Agarwal, Adv. Funct. Mater. 2015, 26(7), 1021-1027.
Thermoresponsive hydrogel fibrous membranes showing directionally controlled movements and surface change with ultra-fast speed are presented for the first time. They show reversible coiling, rolling, bending, and twisting deformations in different controllable directions for many cycles (at least 50 cycles tried) with inside-out change in surfaces and shapes. Speed, reversibility, large-scale deformations and, most importantly, control over the direction of deformation is required in order to make synthetic actuators inspired from natural materials or otherwise. A polymeric synthetic material combining all these properties is still awaited. This issue is addressed and provide a very simple system fulfilling all these requirements by combining porosity and asymmetric swelling/shrinking via orientation of hydrogel fibers at different angles in a fibrous membrane. Electrospinning is used as a tool for making membranes with fibers oriented at different angles.
Unusual and Superfast Temperature-Triggered Actuators
Shaohua Jiang, Fangyao Liu, Arne Lerch, Leonid Ionov, Seema Agarwal Adv. Mater. 2015, 27, 4865–4870.
A superfast actuator based on a bilayer fibrous mat shows folding/unfolding and the formation of 3D structures in a fraction of a second. The actuation is reversible for many cycles without losing its form and size, with unfolding at room temperature and folding above 35 °C. The system is promising for making 3D bioscaffolds, electrodes, and micro-/macroactuators.
Markus Langner, Seema Agarwal, André Baudler, Uwe Schröder and Andreas Greiner Advanced Functional Materials 2015 25(39), 6182-6188.
Exceptionally conductive (250 S cm−1), very fast electrically heatable, thermally insulating, antimicrobial 3D polymeric sponges with very low density (≈30 mg cm−3), superhydrophobicity, and high porosity, their method of preparation, and manifold examples for applications are presented here. The electrical heatability is reversible, reaching 90 °C with 4.4 W in about 19–20 s and cooling immediately on switching off the voltage. The sponges show high contact angles >150° against water on the sponge surface as well as inside the sponge. Water droplets injected into the sponges are ejected. A facile wet-chemical method established for macroscopic melamine–formaldehyde sponges is the key for the thorough in-depth surface metallization of the sponges. The coating thickness and uniformity depend on the metallization formulation, conditions of metallization, and the type of metal used. A scanning electron microscope is used for morphology characterization. A reduced metallization rate in air is highly critical for the in-depth uniform coating of metals. The resulting metallized sponges could be highly interesting for heating as well as insulation devices in addition to oil/water separation membranes.
Paul Pineda Contreras, Christian Kuttner, Andreas Fery, Ullrich Stahlschmidt,
Valérie Jérôme, Ruth Freitag and Seema Agarwal Chem. Commun., 2015, 51, 11899-11902.
A low volume shrinking vinylcyclopropane (VCP) monomer, showing both a high reactivity and a low viscosity, was obtained by applying a sterically hindered and isomeric spacer element, incorporating intermolecular amide hydrogen bonds. The resulting properties locate this VCP system in a pronounced range that so far no other efficient and radical polymerizable resin could enter.
André Baudler, Igor Schmidt, Markus Langner, Andreas Greiner, Uwe Schröder Energy Environ. Sci., 2015, 8, 2048-2055.
Copper and silver are antimicrobial metals, on whose surface bacteria do not grow. As our paper demonstrates, this commonly reported antimicrobial property does not apply to electrochemically active, electrode respiring bacteria. These bacteria readily colonize the surface of these metals, forming a highly active biofilm. Average anodic current densities of 1.1 mA cm−2 (silver) and 1.5 mA cm−2 (copper) are achieved – data that are comparable to that of the benchmark material, graphite (1.0 mA cm−2). Beside the above metals, nickel, cobalt, titanium and stainless steel (SUS 304) were systematically studied towards their suitability as anode materials for microbial fuel cells and related bioelectrochemical systems. The bioelectrochemical data are put in relation to physical data of the materials (specific conductivity, standard potential) and to basic economic considerations. It is concluded that especially copper represents a highly promising anode material, suitable for application in high-performance bioelectrochemical systems.
Z. Fan, M. Köhn Serrano, A. Schaper, S. Agarwal A. Greiner
Adv. Mater.; 2015, 27(26), 3888.
Polymer cages prepared by etching of gold nanoparticles from polymer templates by the “grafting around” method are designed for selective separation of metal nanoparticles. The separation process is demonstrated as a fast biphasic ligand exchange reaction. The high separation efficiency and size selectivity of the polymer cage is verified by comparison with the linear block copolymer.
Ultralight, Soft Polymer Sponges by Self-Assembly of Short Electrospun Fibers in Colloidal Dispersions
Gaigai Duan , Shaohua Jiang , Valérie Jérôme , Joachim H. Wendorff , Amir Fathi , Jaqueline Uhm , Volker Altstädt , Markus Herling , Josef Breu , Ruth Freitag , Seema Agarwal , and Andreas Greiner, Adv. Funct. Mater. 2015, 25, 2850–2856. http://onlinelibrary.wiley.com/doi/10.1002/adfm.201500001/abstract (pdf)
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Ultralight polymer sponges are prepared by freeze-drying of dispersions of short electrospun fi bers. In contrast to many other highly porous materials, these sponges show extremely low densities (<3 mg cm −3 ) in combination with low specifi c surface areas. The resulting hierarchical pore structure of the sponges gives basis for soft and reversibly compressible materials and to hydrophobic behavior in combination with excellent uptake for hydrophobic liquids. Owing to their large porosity, cell culturing is successful after hydrophilic modifi cation of the sponges.
Preparing a pseudo-solid by the reinforcement of polydendate thioether using silver nanoparticles.
H. Pletsch, A. Greiner, S. Agarwal, Nanoscale 2015, 7, 1977-1983.
he design of networks from polymers and noble metal nanoparticles requires thorough control over topological polymer–particle arrangements. This study explores the interaction between a linear polydentate poly(propylene sulfide) (PPrS) ligand and silver nanoparticles (AgNPs) with an aim to study its effect on mechanical and viscoelastic properties. Very low amounts (0.30 vol%) of silver nanoparticles lead to significant mechanical reinforcement of PPrS, yielding viscoelastic properties of an unfastened network with solid-like elastic responses on mechanical stimulation. The materials are made by ring-opening anionic polymerization of propylene sulfide to yield high molar mass PPrS with a total of 593 thioether functionalities per chain, followed by a simple in situ “grafting to” method to homogeneously incorporate AgNPs into the polymer matrix. From investigations on the chain dynamics using dynamic rheology it is concluded that well-dispersed AgNPs impose additional topological constraints on the polymer chains. Calculations of the statistical interparticle distances support a tele-bridging polymer–particle arrangement.
Design of Soft Materials from Triblock Co-Oligomers and Metal Nanoparticles.
H. Pletsch, M. J. Schnepf, S. Agarwal, Chem. Mater. 2014, 26, 4805-4811.
Thermally processable soft material networks with adjustable mechanical properties made from very low molar mass α,ω-dithiol functionalized ABA triblock co-oligomers (α,ω-dithiol oligo(isoprene-b-styrene-b-isoprene) (TISIT)) using AgNP as thermally reversible cross-linking points are highlighted in the present work. Liquid TISIT oligomers were synthesized by sequential anionic polymerization and subsequently cross-linked with AgNP. Low molar masses (4200–4800 g mol–1) were engaged, assuring disordered microstructures and therefore, low viscosities at elevated temperatures. Smooth films with homogeneous nanoparticle distributions of the resulting quasi-segmented soft material networks (TISIT@AgNP) were made by heat pressing. The interplay of styrene and AgNP as the structure-supplying portions in TISIT@AgNP samples facilitates access to materials with tensile strengths up to 5.58 MPa, toughness up to 13.3 MN mm–2, and tensile moduli up to 80.1 MPa at room temperature and strongly decreased elasticity and viscosity at elevated temperatures, even below the glass transition temperature of polystyrene.
Ultrasound-Mediated Synthesis of High-Molecular Weight Polystyrene-Grafted Silver Nanoparticles by Facile Ligand Exchange Reactions in Suspension.
H. Pletsch, L. Peng, F. Mitschang, A. Schaper, M. Hellwig, D. Nette, A. Seubert, A. Greiner, S. Agarwal, Small 2014, 10, 201-208.
Ultrasound mediated facile ligand exchange method in suspension for the formation of polystyrene‒grafted silver nanoparticles is reported. Amazingly, this method allows even grafting of very high molecular weight polystyrenes (up to 217 200 g mol−1) having a single terminal thiol group at the chain end. Detailed studies are carried out to gain insights in the role of molecular weight of the ligands and the mechanism of the ligand exchange reactions. Key factors are determined to be the droplet formation by ultrasonification and low silver content, which enhances the availability of the terminal thiol end group significantly. The extraordinary compatibility of the ligand exchange method in particular regarding high molecular weights is attributed to hydrophilic orientation of the terminal thiol groups at the liquid‒liquid interphase. This is proved conclusively by using an in situ method as a reference approach in which agglomeration occurs at considerably lower molecular weights due to the absence of preferred end group orientation within the polymer coil. In homogeneous phase only the chain length is found to be the crucial factor in stabilization of silver nanoparticles
Tea- Bag- Like Polymer Nanoreactors Filled with Gold Nanoparticles
F. Mitschang, H. Schmalz, S. Agarwal, A. Greiner, Angew. Chem. Int. Ed. 2014, 53, 4972-4975.
Gold-containing polymer nanotubes, which showed both catalytic activity and resistance to leaching, were prepared by the “tubes by fiber templates” (TUFT) process. For this purpose, electrospun polymer nonwovens with incorporated poly(L-lactide)-stabilized gold nanoparticles were coated with poly(p-xylylene) by the chemical vapor deposition process, and then the inner fiber templates were removed. The resulting polymer tubes carried encapsulated gold nanoparticles which were shown to be immobilized and featured pronounced catalytic activity towards the hydrolytic oxidation of dimethylphenylsilane and the alcoholysis of dimethylphenylsilane with n-butanol. The macroscopic nonwovens could be used as tea-bag-like catalyst systems and showed excellent reusability.