Advanced Functional Materials

The design and fabrication of a rolled dielectric elastomer actuator is described and the parametric dependence of the displacement and blocked force on the actuator geometry, elastomer layer thickness, voltage, and number of turns is analyzed. Combinations of different elastomers and carbon nanotube electrodes are investigated and optimized to meet performance characteristics appropriate to tactile display applications, namely operation up to 200 Hz with a combination of a 1 N blocked force and free displacement of 1 mm, all within a volume of less than 1 cm 3. Lives in excess of 50 000 cycles have been obtained. Key to meeting these objectives is control of the multilayering fabrication process, the carbon nanotube electrode concentration, the selection of a soft elastomer with low viscous losses, and a proof-testing procedure for enhancing life cycle reliability.

Scheme 4. Reagents and conditions: a) 2-thienylmagnesium bromide, Ni(dppp)Cl 2 (dppp: 1,3-bis(diphenylphosphino)propane); b) NBS, CHCl 3 / AcOH; c) Pd(PPh 3 ) 4 , 9. 4 J = 1.19 Hz, 2H). 3′-[2-(5-Bromothienyl)]dibromo-2,5″-terthiophene (17): Prepared by bromination of 15 by NBS. m.p. 78°C; 1 H NMR (CDCl 3 ) d = 6.84 (d, 3 J = 3.82 Hz, 1H), 6.89 (d, 3 J = 3.81 Hz, 1H), 6.93 (d, 3 J = 3.84 Hz, 1H), 6.98-6.99 (m, 3H), 7.06 ppm (s, 1H).

Progress towards green and autonomous energy sources includes harnessing living systems and biological tissue. It is recently discovered that the cuticle-cellular tissue bilayer in higher plant leaves functions as an integrated triboelectric generator conductor couple capable of converting mechanical stimuli into electricity. Here, it is investigated for the first time, in detail how charge generation at the living plant leaf occurs, and it is shown how whole plants could be used in plant-hybrid wind-energy harvesting systems. The charge accumulation and compensation in and ex vivo on Rhododendron leaves by Kelvin force microscopy is verified, revealing that charges are induced and transported in living plant tissue whereas charges remain unbalanced and trapped on dead leaves of the same species. A distinct sensing functionality and opportunity to upscale power output is given as electrical signals are species, touch-material, and dose-dependent and scale with frequency, impact force, and area. It is shown that also purely natural mechanical stimuli by wind or self-touching of leaves are converted into electrical signals by a triboelectric mechanism. The entirely plant-enabled and autonomous energy conversion can be used to directly drive light emitting diodes, charge a capacitor, and harvest wind-energy with promise for new energy sources based on the Plant Kingdom.

Recent developments in nanotechnology have led to a method for producing free-standing polymer nanosheets as a macromolecular organization. Compared with bulk films, the large aspect ratio of such nanosheets leads to unique physical properties, such as transparency, noncovalent adhesion, and high flexibility. Here, a biomedical application of polymer nanosheets consisting of biocompatible and biodegradable polysaccharides is reported. Micro-scratch and bulge tests indicate that the nanosheets with a thickness of tens of nanometers have sufficient physical adhesiveness and mechanical strength for clinical use. A nanosheet of 75 nm thickness, a critical load of 9.1 T 10 4 N m À1 , and an elastic modulus of 9.6 GPa is used for the minimally invasive repair of a visceral pleural defect in beagle dogs without any pleural adhesion caused by wound repair. For the first time, clinical benefits of sheettype nano-biomaterials based on molecular organization are demonstrated, suggesting that novel therapeutic tools for overlapping tissue wounds will be possible without the need for conventional surgical interventions.

Time-temperature-transformation (TTT) diagrams are proposed for the crystallization of amorphous metal oxide thin fi lms and their specifi c characteristics are discussed in comparison to glass-based materials, such as glass-ceramics and metallic glasses. The fi lms crystallize from amorphous to full crystallinity in the solid state. As an example the crystallization kinetics for a single-phase metal oxide, ceria, and its gadolinia solid solutions are reported made by the precipitation thin-fi lm method spray pyrolysis. The crystallization of an amorphous metal oxide thin fi lm generally follows the Lijschitz-Sletow-Wagner (LSW) Ostwald ripening theory: Below the percolation threshold of 20 vol% single grains crystallize in the amorphous phase and low crystallization rates are measured. In this state no impact of solute on crystallization is measurable. Once the grains form primary clusters above the threshold the solute slows down crystallization (and grain growth) thus shifting the TTT curves of the doped ceria fi lms to longer times and higher temperatures in comparison to undoped ceria. Current views on crystallization of metal oxide thin fi lms, the impact of solute dragging, and primary TTT diagrams are discussed. Finally, examples on how to use these TTT diagrams for better thermokinetic engineering of metal oxide thin fi lms for MEMS are given, for example, for micro-Solid Oxide Fuel Cells and resistive sensors. In these examples the electrical properties depend on the degree of crystallinity and, thereby, on the TTT conditions.

Organic-inorganic hybrid perovskites (OHPs) are promising emitters for light-emitting diodes (LEDs) due to the high color purity, low cost, and simple synthesis. However, the electroluminescent efficiency of polycrystalline OHP LEDs (PeLEDs) is often limited by poor surface morphology, small exciton binding energy, and long exciton diffusion length of large-grain OHP films caused by uncontrolled crystallization. Here, crystallization of methylammonium lead bromide (MAPbBr 3) is finely controlled by using a polar solvent-soluble self-doped conducting polymer, poly(styrenesulfonate)-grafted polyaniline (PSS-g-PANI), as a hole injection layer (HIL) to induce granular structure, which makes charge carriers spatially confined more effectively than columnar structure induced by the conventional poly(3,4-ethylenedio ythiphene):polystyrenesulfonate (PEDOT:PSS). Moreover, lower acidity of PSS-g-PANI than PEDOT:PSS reduces indium tin oxide (ITO) etching, which releases metallic In species that cause exciton quenching. Finally, doubled device efficiency of 14.3 cd A-1 is achieved for PSS-g-PANI-based polycrystalline MAPbBr 3 PeLEDs compared to that for PEDOT:PSS-based PeLEDs (7.07 cd A-1). Furthermore, PSS-g-PANI demonstrates high efficiency of 37.6 cd A-1 in formamidinium lead bromide nanoparticle LEDs. The results provide an avenue to both control the crystallization kinetics and reduce the migration of In released from ITO by forming OIP films favorable for more radiative luminescence using the polar solvent-soluble and low-acidity polymeric HIL.

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In perovskite solar cells (PSCs), the interfaces of the halide perovskite/ electron transport layer (ETL) and ETL/metal oxide electrode (MOE) always attract and trap free carriers via the surface electrostatic force, altering quasi-Fermi level (E Fq) splitting of contact interfaces, and significantly limit the charge extraction efficiency and intrinsic stability of devices. Herein, a graded "bridge" is first reported to link the MOE and perovskite interfaces by self vertical phase separation doping (PSD), diminishing the side effect of notorious ionic defects via both reinforced interface E bi and the vacancies filling. Experimental and theoretical results prove that the inhomogeneous distribution of CsF in the bulk or surface of PC 61 BM would not only form metal-oxygen (M-O) dipole on MOE, reinforcing the interface E bi , but also create a graded energy bridge to alleviate the disadvantage of band offset raised by the enhanced interface E bi , which significantly avoid the carrier accumulation and recombination at defective interfaces. Employing PSD, the power conversion efficiency of the devices approaches 21% with a high open-circuit voltage (1.148 V) and delivers a high stability of 89% after aging 60 days in atmosphere without encapsulation, which is the highest efficiency of organic electron transport layers for n-i-p PSCs.

The early detection of bone microdamages is crucial to make informed decisions about the therapy and taking precautionary treatments to avoid catastrophic fractures. Conventional computed tomography (CT) imaging faces obstacles in detecting bone microdamages due to the strong self-attenuation of photons from bone and poor spatial resolution. Recent advances in CT technology as well as novel imaging probes can address this problem effectively. Herein, the bone microdamage imaging is demonstrated using ligand-directed nanoparticles in conjunction with photon counting spectral CT. For the first time, Gram-scale synthesis of hafnia (HfO 2) nanoparticles is reported with surface modification by a chelator moiety. The feasibility of delineating these nanoparticles from bone and soft tissue of muscle is demonstrated with photon counting spectral CT equipped with advanced detector technology. The ex vivo and in vivo studies point to the accumulation of hafnia nanoparticles at microdamage site featuring distinct spectral signal. Due to their small sub-5 nm size, hafnia nanoparticles are excreted through reticuloendothelial system organs without noticeable aggregation while not triggering any adverse side effects based on histological and liver enzyme function assessments. These preclinical studies highlight the potential of HfO 2-based nanoparticle contrast agents for skeletal system diseases due to their well-placed K-edge binding energy.

Chronic wounds do not heal in an orderly fashion in part due to the lack of timely release of biological factors essential for healing. Topical administration of various therapeutic factors at different stages is shown to enhance the healing rate of chronic wounds. Developing a wound dressing that can deliver biomolecules with a predetermined spatial and temporal pattern would be beneficial for effective treatment of chronic wounds. Here, an actively controlled wound dressing is fabricated using composite fibers with a core electrical heater covered by a layer of hydrogel containing thermoresponsive drug carriers. The fibers are loaded with different drugs and biological factors and are then assembled using textile processes to create a flexible and wearable wound dressing. These fibers can be individually addressed to enable on-demand release of different drugs with a controlled temporal profile. Here, the effectiveness of the engineered dressing for on-demand release of antibiotics and vascular endothelial growth factor (VEGF) is demonstrated for eliminating bacterial infection and inducing angiogenesis in vitro. The effectiveness of the VEGF release on improving healing rate is also demonstrated in a murine model of diabetic wounds.