All-organic nanocomposites using conducting polypyrrole (PPy) nano-clips as fillers and poly(vinylidene fluoride-chlorotrifluoroethylene) (PVDF-CTFE) as the matrix are studied. The nanocomposites ...with a uniform microstructure were fabricated via a combination of a solution casting and a hot pressing process. Due to the uniform microstructure, the composites exhibit a single glass transition process, whose temperature decreases with increasing PPy content. The dielectric properties of the nanocomposites are systemically studied and analyzed over a wide temperature range from −60 °C to 140 °C and a broad frequency range from 100 Hz to 1 MHz. The nanocomposites have a low percolation threshold (∼7.4 wt%) and exhibit a high dielectric constant and a low dielectric loss. For the composites with 7 wt% of PPy at room temperature, the dielectric constant at 1 kHz is 23 times higher than that of the polymer matrix and the dielectric loss over a broad frequency range is less than 0.4 which is lower than the loss reported in other composites with the composition close to the percolation threshold. It is concluded that mixing PPy with P(VDF-CTFE) results in a new relaxation process that dominates the observed dielectric loss at low temperatures including room temperature. It is demonstrated that it is the DC conductivity rather than the dielectric constant that should be used to determine the percolation threshold.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Analyzing and understanding the structure and morphology of crystalline polymers has been and remains to be a major challenge. Some of the issues have resisted analyses for decades. The present ...account illustrates how individual contributions help build a body of knowledge that must cover length scales ranging from submolecular features to morphology and correlates them with bulk properties. Emphasis is put on structures and morphologies as formed spontaneously. Possible extension of the research area to connected fields is illustrated with a development on supramolecular crystals.
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IJS, KILJ, NUK, PNG, UL, UM
Influences of process conditions on microstructure and dielectric properties of ceramic-polymer composites are systematically studied using CaCu
Ti
O
(CCTO) as filler and P(VDF-TrFE) 55/45 mol.% ...copolymer as the matrix by combining solution-cast and hot-pressing processes. It is found that the dielectric constant of the composites can be significantly enhanced-up to about 10 times - by using proper processing conditions. The dielectric constant of the composites can reach more than 1,000 over a wide temperature range with a low loss (tan δ ~ 10
). It is concluded that besides the dense structure of composites, the uniform distribution of the CCTO particles in the matrix plays a key role on the dielectric enhancement. Due to the influence of the CCTO on the microstructure of the polymer matrix, the composites exhibit a weaker temperature dependence of the dielectric constant than the polymer matrix. Based on the results, it is also found that the loss of the composites at low temperatures, including room temperature, is determined by the real dielectric relaxation processes including the relaxation process induced by the mixing.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
To overcome the low discharging efficiency of ceramic-polymer composites using ferroelectric polymers as matrix and to take the advantage in fabrication offered by the polar polymer, a polar but ...non-ferroelectric polymer – poly(methyl methacrylate) (PMMA) – was selected as the matrix in the development of high performance composites for energy storage. Ba0.5Sr0.5TiO3 (BST) nanoparticles were selected as the filler. Freestanding and flexible BST-PMMA ceramic-polymer nanocomposites with BST content up to 30 vol.% were fabricated in thickness of about 5 μm using spin-coating process and were systemically studied. Due to the strong interaction between the polar groups of PMMA and the hydroxyl groups on the surface of BST nanoparticles, the suspension of BST nanoparticles in PMMA solution exhibits excellent stability and, hence, the nanocomposite films have excellent microstructure uniformity and compatibility between the BST nanoparticles and PMMA matrix. All the BST-PMMA films exhibit excellent frequency (100 Hz to 1 MHz) and temperature (−90 to 100 °C) stabilities in their dielectric properties with a high energy-storage density of more than 11 J/cm3. Most importantly, an ultra-high discharging efficiency of almost 100% is obtained in all the nanocomposites.
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•Non-ferroelectric polar polymer is introduced as matrix for the nanocomposites used as energy-storage dielectrics.•High energy density with ultrahigh discharging efficiency (~100%) are demonstrated by BST-PMMA nanocomposite films.•The BST-PMMA nanocomposite films exhibit excellent temperature and frequency stabilities of dielectric properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Charge transport across metal-molecule interfaces has an important role in organic electronics. Typically, chemical link groups such as thiols or amines are used to bind organic molecules to metal ...electrodes in single-molecule circuits, with these groups controlling both the physical structure and the electronic coupling at the interface. Direct metal-carbon coupling has been shown through C60, benzene and π-stacked benzene, but ideally the carbon backbone of the molecule should be covalently bonded to the electrode without intervening link groups. Here, we demonstrate a method to create junctions with such contacts. Trimethyl tin (SnMe(3))-terminated polymethylene chains are used to form single-molecule junctions with a break-junction technique. Gold atoms at the electrode displace the SnMe(3) linkers, leading to the formation of direct Au-C bonded single-molecule junctions with a conductance that is ∼100 times larger than analogous alkanes with most other terminations. The conductance of these Au-C bonded alkanes decreases exponentially with molecular length, with a decay constant of 0.97 per methylene, consistent with a non-resonant transport mechanism. Control experiments and ab initio calculations show that high conductances are achieved because a covalent Au-C sigma (σ) bond is formed. This offers a new method for making reproducible and highly conducting metal-organic contacts.
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IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Free-standing and translucent nanocomposite films with good flexibility were fabricated using a spin-coating process. BaTiO3 nanoparticles with an average size of about 50 nm and P(VDF-CTFE) ...91/9 mol.% copolymer were used as ceramic fillers and polymer matrix, respectively. Dense and uniform microstructure was obtained due to the good compatibility and homogeneous distribution of BaTiO3 nanoparticles in P(VDF-CTFE) matrix. It was experimentally found that the dielectric constant increased but the breakdown strength decreased with increasing volume fraction of BaTiO3. A dielectric constant of about 53 was obtained in the nanocomposite film with 40 vol.% of BaTiO3, which was about 4.4 times higher than that of the pure P(VDF-CTFE) film. A discharged energy-storage density of 4.9 J/cm3 was obtained in the nanocomposite film with 35 vol.% of BaTiO3 under 2000 kV/cm, which was about 2 times higher than that of the pure P(VDF-CTFE) film under the same electric field.
•BaTiO3-P(VDF-CTFE) nanocomposite films were fabricated using a simple process.•The nanocomposite films were free-standing, flexible and translucent.•Dense and uniform microstructure of the nanocomposite films was obtained.•The dielectric properties and energy-storage performances were investigated.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Strength of structural materials and fibers is usually increased at the expense of strain at failure and toughness. Recent experimental studies have demonstrated improvements in modulus and strength ...of electrospun polymer nanofibers with reduction of their diameter. Nanofiber toughness has not been analyzed; however, from the classical materials property trade-off, one can expect it to decrease. Here, on the basis of a comprehensive analysis of long (5–10 mm) individual polyacrylonitrile nanofibers, we show that nanofiber toughness also dramatically improves. Reduction of fiber diameter from 2.8 μm to ∼100 nm resulted in simultaneous increases in elastic modulus from 0.36 to 48 GPa, true strength from 15 to 1750 MPa, and toughness from 0.25 to 605 MPa with the largest increases recorded for the ultrafine nanofibers smaller than 250 nm. The observed size effects showed no sign of saturation. Structural investigations and comparisons with mechanical behavior of annealed nanofibers allowed us to attribute ultrahigh ductility (average failure strain stayed over 50%) and toughness to low nanofiber crystallinity resulting from rapid solidification of ultrafine electrospun jets. Demonstrated superior mechanical performance coupled with the unique macro-nano nature of continuous nanofibers makes them readily available for macroscopic materials and composites that can be used in safety-critical applications. The proposed mechanism of simultaneously high strength, modulus, and toughness challenges the prevailing 50 year old paradigm of high-performance polymer fiber development calling for high polymer crystallinity and may have broad implications in fiber science and technology.
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IJS, KILJ, NUK, PNG, UL, UM
Self-assembly of rigid building blocks with explicit shape and symmetry is substantially influenced by the geometric factors and remains largely unexplored. We report the selective assembly behaviors ...of a class of precisely defined, nanosized giant tetrahedra constructed by placing different polyhedral oligomeric silsesquioxane (POSS) molecular nanoparticles at the vertices of a rigid tetrahedral framework. Designed symmetry breaking of these giant tetrahedra introduces precise positional interactions and results in diverse selectively assembled, highly ordered supramolecular lattices including a Frank-Kasper A15 phase, which resembles the essential structural features of certain metal alloys but at a larger length scale. These results demonstrate the power of persistent molecular geometry with balanced enthalpy and entropy in creating thermodynamically stable supramolecular lattices with properties distinct from those of other self-assembling soft materials.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Summary
This paper proposes a novel multidimensional composite periodic foundation for seismic isolation. The composite periodic foundation achieves multidimensional attenuation by innovative ...arrangement of periodic structures and taking advantage of the directional attenuation zone of periodic structures. Directional attenuation zones of periodic structures are derived for the in‐plane wave, and the impact of geometrical parameters of the periodic structure on the characteristics of the directional attenuation zones is studied. The effectiveness of the proposed composite periodic foundation is demonstrated through application in seismic isolation for nuclear power plant structures. Harmonic analysis and time history analysis results show that the proposed composite periodic foundation with low‐frequency directional attenuation zones can effectively reduce vibrations of the upper structure in both horizontal and vertical directions.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Neutrophil extracellular traps (NETs) are beneficial antimicrobial defense structures that can help fight against invading pathogens in the host. However, recent studies reveal that NETs exert ...adverse effects in a number of diseases including those of the lung. Many inflammatory lung diseases are characterized with a massive influx of neutrophils into the airways. Neutrophils contribute to the pathology of these diseases. To date, NETs have been identified in the lungs of cystic fibrosis (CF), acute lung injury (ALI), allergic asthma, and lungs infected with bacteria, virus, or fungi. These microbes and several host factors can stimulate NET formation, or NETosis. Different forms of NETosis have been identified and are dependent on varying types of stimuli. All of these pathways however appear to result in the formation of NETs that contain DNA, modified extracellular histones, proteases, and cytotoxic enzymes. Some of the NET components are immunogenic and damaging to host tissue. Innate immune collectins, such as pulmonary surfactant protein D (SP-D), bind NETs, and enhance the clearance of dying cells and DNA by alveolar macrophages. In many inflammatory lung diseases, bronchoalveolar SP-D levels are altered and its deficiency results in the accumulation of DNA in the lungs. Some of the other therapeutic molecules under consideration for treating NET-related diseases include DNases, antiproteases, myeloperoxidase (MPO) inhibitors, peptidylarginine deiminase-4 inhibitors, and anti-histone antibodies. NETs could provide important biological advantage for the host to fight against certain microbial infections. However, too much of a good thing can be a bad thing. Maintaining the right balance of NET formation and reducing the amount of NETs that accumulate in tissues are essential for harnessing the power of NETs with minimal damage to the hosts.
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