pinecone/core-2020-05-10-deduplication huggingface dataset:
Synthesis and thermoelectric characterization of Bi2Te3 nanoparticles

We report a novel synthesis for near monodisperse, sub-10-nm Bi2Te3
nanoparticles. At first, a new reduction route to bismuth nanoparticles is
described which are applied as starting materials in the formation of
rhombohedral Bi2Te3 nanoparticles. After ligand removal by a novel hydrazine
hydrate etching procedure, the nanoparticle powder is spark plasma sintered to
a pellet with preserved crystal grain sizes. Unlike previous works on the
properties of Bi2Te3 nanoparticles, the full thermoelectric characterization of
such sintered pellets shows a highly reduced thermal conductivity and the same
electric conductivity as bulk n-type Bi2Te3.Comment: 8 pages, 8 figures, 1 tabl
High Electromechanical Response of Ionic Polymer Actuators with Controlled-Morphology Aligned Carbon Nanotube/Nafion Nanocomposite Electrodes

Recent advances in fabricating controlled-morphology vertically aligned carbon nanotubes (VA-CNTs) with ultrahigh volume fraction create unique opportunities for markedly improving the electromechanical performance of ionic polymer conductor network composite (IPCNC) actuators. Continuous paths through inter-VA-CNT channels allow fast ion transport, and high electrical conduction of the aligned CNTs in the composite electrodes lead to fast device actuation speed (>10% strain/second). One critical issue in developing advanced actuator materials is how to suppress the strain that does not contribute to the actuation (unwanted strain) thereby reducing actuation efficiency. Here, experiments demonstrate that the VA-CNTs give an anisotropic elastic response in the composite electrodes, which suppresses the unwanted strain and markedly enhances the actuation strain (>8% strain under 4 V). The results reported here suggest pathways for optimizing the electrode morphology in IPCNCs using ultrahigh volume fraction VA-CNTs to further enhanced performance.Author Manuscript 2011 October 8United States. Army Research Office (Grant W911NF-07-1-0452)National Institutes of Health (U.S.) (Grant R01-EY018387-02)United States. Multidisciplinary University Research Initiativ
High-Energy Al/CuO Nanocomposites Obtained by DNA-Directed Assembly

Over the next few years, it is expected that new, energetic, multifunctional materials will be engineered. There is a need for new methods to assemble such materials from manufactured nanopowders. In this article, we demonstrate a DNA-directed assembly procedure to produce highly energetic nanocomposites by assembling Al and CuO nanoparticles into micrometer-sized particles of an Al/CuO nanocomposite, which has exquisite energetic performance in comparison with its physically mixed Al/CuO counterparts. Using 80 nm Al nanoparticles, the heat of reaction and the onset temperature are 1.8 kJ g-1 and 410 degrees C, respectively. This experimental achievement relies on the development of simple and reliable protocols to disperse and sort metallic and metal oxide nanopowders in aqueous solution and the establishment of specific DNA surface-modification processes for Al and CuO nanoparticles. Overall, our work, which shows that DNA can be used as a structural material to assemble Al/Al, CuO/CuO and Al/CuO composite materials, opens a route for molecular engineering of the material on the nanoscale
A Biologically Active Surface Enzyme Assembly that Attenuates Thrombus Formation

Activation of hemostatic pathways by blood‐contacting materials remains a major hurdle in the development of clinically durable artificial organs and implantable devices. Here, it is postulated that surface‐induced thrombosis may be attenuated by the reconstitution onto blood contacting surfaces of bioactive enzymes that regulate the production of thrombin, a central mediator of both coagulation and platelet activation cascades. Thrombomodulin (TM), a transmembrane protein expressed by endothelial cells, is an established negative regulator of thrombin generation in the circulatory system. Traditional techniques to covalently immobilize enzymes on solid supports may modify residues contained within or near the catalytic site, thus reducing the bioactivity of surface enzyme assemblies. In this report, a molecular engineering and bioorthogonal chemistry approach to site‐specifically immobilize a biologically active recombinant human TM fragment onto the luminal surface of small diameter prosthetic vascular grafts is presented. Bioactivity and biostability of TM modified grafts is confirmed in vitro and the capacity of modified grafts to reduce platelet activation is demonstrated using a non‐human primate model. These studies indicate that molecularly engineered interfaces that display TM actively limit surface‐induced thrombus formation.     A biologically active thrombomodulin surface assembly  to limit interfacial thrombin production was generated on the lumen of clinical ePTFE vascular grafts by site‐specific covalent immobilization. Therapeutic capacity of this biomimetic surface engineering approach to attenuate thrombus formation was demonstrated in a clinically relevant in vivo model of prosthetic graft thrombosis
Organic Dye Design Tools for Efficient Photocurrent Generation in Dye‐Sensitized Solar Cells: Exciton Binding Energy and Electron Acceptors

The relationship between the exciton binding energies of several pure organic dyes and their chemical structures is explored using density functional theory calculations in order to optimize the molecular design in terms of the light‐to‐electric energy‐conversion efficiency in dye‐sensitized solar cell devices. Comparing calculations with measurements reveals that the exciton binding energy and quantum yield are inversely correlated, implying that dyes with lower exciton binding energy produce electric current from the absorbed photons more efficiently. When a strong electron‐accepting moiety is inserted in the middle of the dye framework, the light‐to‐electric energy‐conversion behavior significantly deteriorates. As verified by electronic‐structure calculations, this is likely due to electron localization near the electron‐deficient group. The combined computational and experimental design approach provides insight into the functioning of organic photosensitizing dyes for solar‐cell applications. This is exemplified by the development of a novel, all‐organic dye (EB‐01) exhibiting a power conversion efficiency of over 9%.     A combined computational and experimental design approach  provides insight into the functioning of organic photosensitizer dyes for solar cell applications. Comparing calculations with measurements reveals that the exciton binding energy and quantum yield are inversely correlated. When a strong electron‐accepting moiety is inserted in the middle of the dye framework, the light‐to‐electric energy conversion behavior significantly deteriorates
Design Principle of Conjugated Polyelectrolytes to Make Them Water‐Soluble and Highly Emissive

The correlation between the molecular design of a conjugated polyelectrolyte (CPE) and its aggregated structure and the emissive properties in water is systematically investigated by means of UV–vis spectrometry, fluorescence spectroscopy, and scanning/transmission electron microscopy. Five different and rationally designed CPEs having carboxylic acid side chains are synthesized. All five conjugated polyelectrolytes are seemingly completely soluble in water in visual observation. However, their quantum yields are dramatically different, changing from 0.45 to 51.4%. Morphological analysis by electron microscopy combined with fluorescence spectrophotometry reveals that the CPEs form self‐assembled aggregates at the nanoscale depending on the nature of their side chains. The feature of the self‐assembled aggregates directly determines the emissive property of the CPEs. The nature and the length of the spacer between the carboxylic acid group and the CPE backbone have a strong influence on the quantum yield of the CPEs. Our study demonstrates that bulky and hydrophilic side chains and spacers are required to achieve complete water‐solubility and high quantum yield of CPEs in water, providing an important molecular design principle to develop functional CPEs.     The correlation between the molecular design of conjugated polyelectrolytes  (CPEs) and their solubility and emissive properties in water is systematically investigated by means of UV–vis and fluorescence spectroscopy and electron microscopy. Bulky and hydrophilic side chains and spacers are required to achieve complete water solubility and high quantum yield of CPEs in water, providing an important molecular design principle to develop functional CPEs
Photoclickable surfaces for profluorescent covalent polymer coatings

The nitrile imine-mediated tetrazole-ene cycloaddition reaction (NITEC) is introduced as a powerful and versatile conjugation tool to covalently ligate macromolecules onto variable (bio)surfaces. The NITEC approach is initiated by UV irradiation and proceeds rapidly at ambient temperature yielding a highly fluorescent linkage. Initially, the formation of block copolymers by the NITEC methodology is studied to evidence its efficacy as a macromolecular conjugation tool. The grafting of polymers onto inorganic (silicon) and bioorganic (cellulose) surfaces is subsequently carried out employing the optimized reaction conditions obtained from the macromolecular ligation experiments and evidenced by surface characterization techniques, including X-ray photoelectron spectroscopy and FT-IR microscopy. In addition, the patterned immobilization of variable polymer chains onto profluorescent cellulose is achieved through a simple masking process during the irradiation. Photoinduced nitrile imine-alkene 1,3-dipolar cycloaddition (NITEC) is employed to covalently bind well-defined polymers onto silicon oxide or cellulose. A diaryl tetrazole-functionalized molecule is grafted via silanization or amidification, respectively. Under UV light, a reactive nitrile imine rapidly forms and reacts with maleimide-functionalized polymers yielding a fluorescent linkage. Via a masking method, polymeric fluorescent patterns are achieved
Photoconductive Hybrid Films via Directional Self‐Assembly of C 60  on Aligned Carbon Nanotubes

Hybrid nanostructured materials can exhibit different properties than their constituent components, and can enable decoupled engineering of energy conversion and transport functions. Novel means of building hybrid assemblies of crystalline C 60  and carbon nanotubes (CNTs) are presented, wherein aligned CNT films direct the crystallization and orientation of C 60  rods from solution. In these hybrid films, the C 60  rods are oriented parallel to the direction of the CNTs throughout the thickness of the film. High‐resolution imaging shows that the crystals incorporate CNTs during growth, yet grazing‐incidence X‐ray diffraction (GIXD) shows that the crystal structure of the C 60  rods is not perturbed by the CNTs. Growth kinetics of the C 60  rods are enhanced 8‐fold on CNTs compared to bare Si, emphasizing the importance of the aligned, porous morphology of the CNT films as well as the selective surface interactions between C 60  and CNTs. Finally, it is shown how hybrid C 60 –CNT films can be integrated electrically and employed as UV detectors with a high photoconductive gain and a responsivity of 10 5  A W −1  at low biases (± 0.5 V). The finding that CNTs can induce rapid, directional crystallization of molecules from solution may have broader implications to the science and applications of crystal growth, such as for inorganic nanocrystals, proteins, and synthetic polymers.     Aligned carbon nanotube (CNT) films cause rapid, directional crystallization of C 60  rods  from solution, resulting in hybrid structures where the C 60  rods incorporate CNTs during growth and are oriented parallel to the direction of the CNTs. The hybrid sheets are integrated electrically and employed as UV detectors with high photoconductive gain (responsivity as high as 10 5  A W −1  at low biases (±0.5 V))
Colorimetric Detection of Warfare Gases by Polydiacetylenes Toward Equipment‐Free Detection

Rationally designed polydiacetylene (PDA) molecules have been developed for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate (OP) nerve agents, a mass destruction weapon. Oxime (OX) functionality was incorporated into diacetylene molecules to utilize its strong affinity toward organophosphates. The diacetylene molecules having an OX functional group (OX‐PDA) were self‐assembled to form PDA liposomes in an aqueous solution. Upon exposure to organophosphate nerve agent simulants, OX at the OX‐PDA liposome surface interacts with nerve agent simulants, which results in intraliposomal repulsive stress due to steric repulsion between OP‐occupied OX units at the liposome surface as well as interliposomal aggregation induced by increased hydrophobicity of the liposome surface via OP‐OX complex formation. The resulting intra‐ and interliposomal stress causes disturbance of the conjugated backbone of OX‐PDA, producing color change as a label‐free and sensitive sensory signal. The effects of molecular structure on selectivity and sensitivity of OX‐PDA liposome solution, OX‐PDA liposome‐embedded agarose gels, and OX‐PDA liposome‐coated cellulose acetate membranes were systematically investigated. The optimized OX‐PDA liposome in the solid state showed selective and rapid optical transition upon exposure down to 160 ppb of diisopropylfluorophosphate (DFP), a nerve agent simulant. The results provide an insightful molecular design principle of PDA‐based colorimetric sensor and suggest portable sensory patches for rapid, selective, sensitive, and convenient colorimetric detection of organophosphate nerve agents.     Polydiacetylene (PDA) liposomes having oxime (OX) functionality  are rationally designed and synthesized to selectively and sensitively detect organophosphate (OP) nerve agents. Solutions, gel‐pads, and solid films of OX‐PDA liposome demonstrate convenient, rapid, selective, and sensitive colorimetric detection of nerve agent simulants through intra‐liposomal repulsion and interliposomal hydrophobic aggregation
Elastomeric Origami: Programmable Paper-Elastomer Composites as Pneumatic Actuators

The development of soft pneumatic actuators based on composites consisting of elastomers with embedded sheet or fiber structures (e.g., paper or fabric) that are flexible but not extensible is described. On pneumatic inflation, these actuators move anisotropically, based on the motions accessible by their composite structures. They are inexpensive, simple to fabricate, light in weight, and easy to actuate. This class of structure is versatile: the same principles of design lead to actuators that respond to pressurization with a wide range of motions (bending, extension, contraction, twisting, and others). Paper, when used to introduce anisotropy into elastomers, can be readily folded into 3D structures following the principles of origami; these folded structures increase the stiffness and anisotropy of the elastomeric actuators, while being light in weight. These soft actuators can manipulate objects with moderate performance; for example, they can lift loads up to 120 times their weight. They can also be combined with other components, for example, electrical components, to increase their functionality.Chemistry and Chemical Biolog
A facile approach to chemically modified graphene and its polymer nanocomposites

A scalable approach for the mass production of chemically modified graphene has yet to be developed, which holds the key to the large-scale production of stable graphene colloids for optical electronics energy conversion and storage materials, catalysis, sensors, composite, etc. Here a facile approach to fabricating covalently modified graphene and its polymer nanocomposites is presented. The method involves: i)employing a common furnace, rather than a furnace installed with a quartz tube and operated in inert gas as required in previous studies, to treat a commercial graphite interrelation compound with thermal shocking and ultrasonication  and fabricate graphene platelets (GnPs) with a thickness of 2.51+-0.39nm that contain only 7 at% oxygen; ii)grafting these GnPs with commercial, long-chain surfactant which is able to create molecular entanglement with polymer matrixes by taking advantage of the reactions between the epoxide groups of the platelets and the end amine groups of the surfactant to produce chemically modified graphehe platelets (m-GnPs); and iii)solution-mixing m-GnPs with a commonly used polymer to fabricate nanocomposites. These m-GnPs are well dispered in a polymer with imrpoved mechanical properties and a low percolation threshold of electrical conductivity at 0.25col%. This novel approach could lead to the future scalable production of graphehe and its nanocomposites
Colossal Thermoelectric Power Factor in K$_{7/8}$RhO$_2$

We discuss the thermoelectric and optical properties of layered
K$_{x}$RhO$_{2}$ (\emph{x} = 1/2 and 7/8) in terms of the electronic structure
determined by first principles calculations as well as Boltzmann transport
theory. Our optimized lattice constants differ significantly from the
experiment, but result in optical and transport properties close to the
experiment. The main contribution to the optical spectra are due to intra and
inter-band transitions between the Rh 4\emph{d} and O 2\emph{p} states. We find
a similar power factor for pristine K$_{x}$RhO$_{2}$ at low and high cation
concentartions. Our transport results of hydrated K$_{x}$RhO$_{2}$ at room
temperature show highest value of the power factor among the hole-type
materials. Specially at 100 K, we obtain a value of 3$\times$10$^{-3}$ K$^{-1}$
for K$_{7/8}$RhO$_{2}$, which is larger than that of Na$_{0.88}$CoO$_{2}$ {[}M.
Lee \emph{et al}., Nat. Mater. 5, 537 (2006){]}. In general, the electronic and
optical properties of K$_{x}$RhO$_{2}$ are similar to Na$_{x}$CoO$_{2}$ with
enhanced transport properties in the hydrated phase
Charge density dependent nongeminate recombination in organic bulk
  heterojunction solar cells

Apparent recombination orders exceeding the value of two expected for
bimolecular recombination have been reported for organic solar cells in various
publications. Two prominent explanations are bimolecular losses with a carrier
concentration dependent prefactor due to a trapping limited mobility, and
protection of trapped charge carriers from recombination by a donor--acceptor
phase separation until reemission from these deep states. In order to clarify
which mechanism is dominant we performed temperature and illumination dependent
charge extraction measurements under open circuit as well as short circuit
conditions at poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C$_{61}$butyric acid
methyl ester (P3HT:PC$_{61}$BM) and PTB7:PC$_{71}$BM
(Poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]])
solar cells in combination with current--voltage characteristics. We show that
the charge carrier density $n$ dependence of the mobility $\mu$ and the
recombination prefactor are different for PC$_{61}$BM at temperatures below
300K and PTB7:PC$_{71}$BM at room temperature. Therefore, in addition to
$\mu(n)$ a detrapping limited recombination in systems with at least partial
donor--acceptor phase separation is required to explain the high recombination
orders.Comment: 7 pages, 4 figure
Halogen Bonding versus Hydrogen Bonding in Driving Self-Assembly and Performance of Light-Responsive Supramolecular Polymers

Halogen bonding is arguably the least exploited among the many non-covalent interactions used in dictating molecular self-assembly. However, its directionality renders it unique compared to ubiquitous hydrogen bonding. Here, the role of this directionality in controlling the performance of light-responsive supramolecular polymers is highlighted. In particular, it is shown that light-induced surface patterning, a unique phenomenon occurring in azobenzene-containing polymers, is more efficient in halogen-bonded polymer–azobenzene complexes than in the analogous hydrogen-bonded complexes. A systematic study is performed on a series of azo dyes containing different halogen or hydrogen bonding donor moieties, complexed to poly(4-vinylpyridine) backbone. Through single-atom substitution of the bond-donor, control of both the strength and the nature of the noncovalent interaction between the azobenzene units and the polymer backbone is achieved. Importantly, such substitution does not significantly alter the electronic properties of the azobenzene units, hence providing us with unique tools in studying the structure–performance relationships in the light-induced surface deformation process. The results represent the first demonstration of light-responsive halogen-bonded polymer systems and also highlight the remarkable potential of halogen bonding in fundamental studies of photoresponsive azobenzene-containing polymers
One-Step Multipurpose Surface Functionalization by Adhesive Catecholamine

Surface modification is one of the most important techniques in modern science and engineering. The facile introduction of a wide variety of desired properties onto virtually any material surface is an ultimate goal in surface chemistry. To achieve this goal, the incorporation of structurally diverse molecules onto any material surface is an essential capability for ideal surface modification. Here, a general strategy for surface modification is presented in which many diverse surfaces can be functionalized by immobilizing a wide variety of molecules. This strategy functionalizes surfaces by a one-step immersion of substrates in a one-pot mixture of a molecule and a catecholamine surface modification agent. This one-step procedure for surface modification represents a standard protocol to control interfacial properties.Armed Forces Institute of Regenerative Medicine (Award W81XWH-08-2-0034)National Institutes of Health (U.S.) (2R01DE016516-06
Composite Dissolving Microneedles for Coordinated Control of Antigen and Adjuvant Delivery Kinetics in Transcutaneous Vaccination

Transcutaneous administration has the potential to improve therapeutics delivery, providing an approach that is safer and more convenient than traditional alternatives, while offering the opportunity for improved therapeutic efficacy through sustained/controlled drug release. To this end, a microneedle materials platform is demonstrated for rapid implantation of controlled-release polymer depots into the cutaneous tissue. Arrays of microneedles composed of drug-loaded poly(lactide-co-glycolide) (PLGA) microparticles or solid PLGA tips are prepared with a supporting and rapidly water-soluble poly(acrylic acid) (PAA) matrix. Upon application of microneedle patches to the skin of mice, the microneedles perforate the stratum corneum and epidermis. Penetration of the outer skin layers is followed by rapid dissolution of the PAA binder on contact with the interstitial fluid of the epidermis, implanting the microparticles or solid polymer microneedles in the tissue, which are retained following patch removal. These polymer depots remain in the skin for weeks following application and sustain the release of encapsulated cargos for systemic delivery. To show the utility of this approach the ability of these composite microneedle arrays to deliver a subunit vaccine formulation is demonstrated. In comparison to traditional needle-based vaccination, microneedle delivery gives improved cellular immunity and equivalent generation of serum antibodies, suggesting the potential of this approach for vaccine delivery. However, the flexibility of this system should allow for improved therapeutic delivery in a variety of diverse contexts.Massachusetts Institute of Technology. Ragon Institute of MGH, MIT and HarvardNational Institutes of Health (U.S.) (Award AI095109)United States. Army Research Office (Contract W911NF-07-D-0004