Showing papers in "Advanced Functional Materials in 2007"
TL;DR: Recent research progress on the design of functional MSN materials with various mechanisms of controlled release, along with the ability to achieve zero release in the absence of stimuli, and the introduction of new characteristics to enable the use of nonselective molecules as screens for the construction of highly selective sensor systems are reviewed.
Abstract: Recent advancements in morphology control and surface functionalization of mesoporous silica nanoparticles (MSNs) have enhanced the biocompatibility of these materials with high surface areas and pore volumes. Several recent reports have demonstrated that the MSNs can be efficiently internalized by animal and plant cells. The functionalization of MSNs with organic moieties or other nanostructures brings controlled release and molecular recognition capabilities to these mesoporous materials for drug/gene delivery and sensing applications, respectively. Herein, we review recent research progress on the design of functional MSN materials with various mechanisms of controlled release, along with the ability to achieve zero release in the absence of stimuli, and the introduction of new characteristics to enable the use of nonselective molecules as screens for the construction of highly selective sensor systems.
1,574 citations
TL;DR: In this paper, the self-organization of the polymer in solar cells based on regioregular poly(3-hexylthiophene) (RR-P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) is studied systematically as a function of the spin-coating time.
Abstract: The self-organization of the polymer in solar cells based on regioregular poly(3-hexylthiophene) (RR-P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) is studied systematically as a function of the spin-coating time ts (varied from 20–80 s), which controls the solvent annealing time ta, the time taken by the solvent to dry after the spin-coating process. These blend films are characterized by photoluminescence spectroscopy, UV-vis absorption spectroscopy, atomic force microscopy, and grazing incidence X-ray diffraction (GIXRD) measurements. The results indicate that the π-conjugated structure of RR-P3HT in the films is optimally developed when ta is greater than 1 min (ts ∼ 50 s). For ts < 50 s, both the short-circuit current (JSC) and the power conversion efficiency (PCE) of the corresponding polymer solar cells show a plateau region, whereas for 50 < ts < 55 s, the JSC and PCE values are significantly decreased, suggesting that there is a major change in the ordering of the polymer in this time window. The PCE decreases from 3.6 % for a film with a highly ordered π-conjugated structure of RR-P3HT to 1.2 % for a less-ordered film. GIXRD results confirm the change in the ordering of the polymer. In particular, the incident photon-to-electron conversion efficiency spectrum of the less-ordered solar cell shows a clear loss in both the overall magnitude and the long-wavelength response. The solvent annealing effect is also studied for devices with different concentrations of PCBM (PCBM concentrations ranging from 25 to 67 wt %). Under “solvent annealing” conditions, the polymer is seen to be ordered even at 67 wt % PCBM loading. The open-circuit voltage (VOC) is also affected by the ordering of the polymer and the PCBM loading in the active layer.
1,165 citations
TL;DR: In this article, the performance of α-Fe2O3 nanoflakes has been evaluated by cyclic voltammery, galvanostatic discharge-charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature.
Abstract: Nanoflakes of α-Fe2O3 were prepared on Cu foil by using a thermal treatment method. The nanoflakes were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The reversible Li-cycling properties of the α-Fe2O3 nanoflakes have been evaluated by cyclic voltammery, galvanostatic discharge–charge cycling, and impedance spectral measurements on cells with Li metal as the counter and reference electrodes, at ambient temperature. Results show that Fe2O3 nanoflakes exhibit a stable capacity of (680 ± 20) mA h g–1, corresponding to (4.05 ± 0.05) moles of Li per mole of Fe2O3 with no noticeable capacity fading up to 80 cycles when cycled in the voltage range 0.005–3.0 V at 65 mA g–1 (0.1 C rate), and with a coulombic efficiency of > 98 % during cycling (after the 15th cycle). The average discharge and charge voltages are 1.2 and 2.1 V, respectively. The observed cyclic voltammograms and impedance spectra have been analyzed and interpreted in terms of the ‘conversion reaction' involving nanophase Fe0–Li2O. The superior performance of Fe2O3 nanoflakes is clearly established by a comparison of the results with those for Fe2O3 nanoparticles and nanotubes reported in the literature.
1,009 citations
TL;DR: In this article, the percolation threshold of carbon nanotube (CNT)-reinforced polymer nanocomposites is investigated based on an interparticle distance concept.
Abstract: Critical factors that determine the percolation threshold of carbon nanotube (CNT)-reinforced polymer nanocomposites are studied. An improved analytical model is developed based on an interparticle distance concept. Two dispersion parameters are introduced in the model to correctly reflect the different dispersion states of CNTs in the matrix—entangled bundles and well-dispersed individual CNTs. CNT–epoxy nanocomposites with different dispersion states are fabricated from the same constituent materials by employing different processing conditions. The corresponding percolation thresholds of the nanocomposites vary over a wide range, from 0.1 to greater than 1.0 wt %, and these variations are explained in terms of dispersion parameters and aspect ratios of CNTs. Important factors that control the percolation threshold of nanocomposites are identified based on the comparison between modeling data and experimental results.
958 citations
TL;DR: In this article, a hierarchical carbon monolith with both mesopores and macropores was successfully prepared by using meso-/macroporous silica as a template and using mesophase pitch as a precursor.
Abstract: In this paper, we report on Li storage in hierarchically porous carbon monoliths with a relatively higher graphite-like ordered carbon structure. Macroscopic carbon monoliths with both mesopores and macropores were successfully prepared by using meso-/macroporous silica as a template and using mesophase pitch as a precursor. Owing to the high porosity (providing ionic transport channels) and high electronic conductivity (ca. 0.1 S cm–1), this porous carbon monolith with a mixed conducting 3D network shows a superior high-rate performance if used as anode material in electrochemical lithium cells. A challenge for future research as to its applicability in batteries is the lowering of the irreversible capacity.
674 citations
TL;DR: In this paper, the hierarchical macro-mesoporous structures of titania can spontaneously form by self-assembly in alkoxide-water solutions in the absence of organic templates or auxiliary additives.
Abstract: Hierarchical macro-/mesoporous titania is prepared without the addition of templates or auxiliary additives at room temperature by the simple dropwise addition of tetrabutyl titanate to pure water, and then calcined at various temperatures. The products are characterized by X-ray diffraction, N 2 -adsorption-desorption analysis, scanning electron microscopy, and the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of acetone in air. The results reveal that hierarchical macro-/mesoporous structures of titania can spontaneously form by self-assembly in alkoxide-water solutions in the absence of organic templates or auxiliary additives. The calcination temperature has a strong effect on the structures and photocatalytic activity of the prepared titania. At 300 °C, the calcined sample shows the highest photocatalytic activity. At 400 and 500 °C, the photocatalytic activity slightly decreases. When the calcination temperature is higher than 500 °C, the photocatalytic activity greatly decreases because of the destruction of the hierarchical macro-/mesoporous structure of the titania and the drastic decrease of specific surface area. The hierarchically macro-/mesostructured titania network with open and accessible pores is well-preserved after calcination at 500 °C, indicating especially high thermal stability. The macroporous channel structures are even preserved after calcination at 800 °C. This hierarchical macro-/mesostructured titania is significant because of its potential applications in photocatalysis, catalysis, solar-cell, separation, and purification processes.
632 citations
TL;DR: In this paper, a simple model that reproduces the steady-state and transient response of OECTs by considering these devices in terms of an ionic and an electronic circuit is presented.
Abstract: In recent years, organic electrochemical transistors (OECTs) have emerged as attractive devices for a variety of applications, particularly in the area of sensing. While the electrical characteristics of OECTs are analogous to those of conventional organic field effect transistors, appropriate models for OECTs have not yet been developed. In particular, little is known about the transient characteristics of OECTs, which are determined by a complex interplay between ionic and electronic motion. In this paper a simple model is presented that reproduces the steady-state and transient response of OECTs by considering these devices in terms of an ionic and an electronic circuit. A simple analytical expression is derived that can be used to fit steady-state OECT characteristics. For the transient regime, comparison with experimental data allowed an estimation of the hole mobility in poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate). This work paves the way for rational optimization of OECTs.
592 citations
TL;DR: In this paper, the capacity of nano-ZnCo2O4 was investigated in terms of the capacity contribution of Zn through both alloy formation and displacement reaction, and it was shown that both Zn- and Co-ions act as mutual beneficial matrices and reversible capacity contribution was achieved through both de-alloying and displacement reactions, which is consistent with a reaction mechanism for Li-recyclability.
Abstract: ZnCo2O4 has been synthesized by the low-temperature and cost-effective urea combustion method. X-ray diffraction (XRD), HR-TEM and selected area electron diffraction (SAED) studies confirmed its formation in pure and nano-phase form with particle size ∼ 15–20 nm. Galvanostatic cycling of nano-ZnCo2O4 in the voltage range 0.005–3.0 V versus Li at 60 mA g–1 gave reversible capacities of 900 and 960 mA h g–1, when cycled at 25 °C and 55 °C, respectively. These values correspond to ∼ 8.3 and ∼ 8.8 mol of recyclable Li per mole of ZnCo2O4. Almost stable cycling performance was exhibited in the range 5–60 cycles at 60 mA g–1 and at 25 °C with ∼ 98 % coulombic efficiency. A similar cycling stability at 55 °C, and good rate-capability both at 25 and 55 °C were found. The average discharge- and charge-potentials were ∼ 1.2 V and ∼ 1.9 V, respectively. The ex-situ-XRD, -HRTEM, -SAED and galvanostatic cycling data are consistent with a reaction mechanism for Li-recyclability involving both de-alloying-alloying of Zn and displacement reactions, viz., LiZn ↔ Zn ↔ ZnO and Co ↔ CoO ↔ Co3O4. For the first time we have shown that both Zn- and Co-ions act as mutual beneficial matrices and reversible capacity contribution of Zn through both alloy formation and displacement reaction takes place to yield stable and high capacities. Thus, nano-ZnCo2O4 ranks among the best oxide materials with regard to Li-recyclability.
570 citations
TL;DR: In this article, a series of starburst triarylamine fluorophores SBCHO, DBCHO and CZCHO were investigated as non-doped host emitters and hole transporters.
Abstract: A new series of starburst triarylamine fluorophores SBCHO, DBCHO, CZCHO, CZCN, and SBCN, that incorporate diphenylamine or carbazole as the electron donor and dicyanovinyl or aldehyde as the electron acceptor, has been prepared and their photophysical properties are investigated. In sharp contrast to most red-emitting dopants, which show serious aggregation-caused quench phenomena, the new starburst triphenylamine derivatives reported here show unique enhanced emission in the solid state or upon aggregation. Organic light emitting diodes using these compounds as non-doped host emitters and hole transporters have been fabricated. The highest external quantum yield reaches 2.09 % for CZCHO. SBCHO was investigated as a chlorine gas fluorescence (FL) solid-film sensor for the first time. The high-intensity emission was ‘turned off' immediately after being blown by Cl2 gas.
512 citations
TL;DR: In this article, a facile and one-pot synthesis of Cu2O microspheres with multilayered and porous shells, which were organized by nanocrystals, was presented.
Abstract: Hierarchical assembly of hollow microstructures is of great scientific and practical value and remains a great challenge. This paper presents a facile and one-pot synthesis of Cu2O microspheres with multilayered and porous shells, which were organized by nanocrystals. The time-dependent experiments revealed a two-step organization process, in which hollow microspheres of Cu-2(OH)(3)NO3 were formed first due to the Ostwald ripening and then reduced by glutamic acid, the resultant Cu2O nanocrystals were deposited on the hollow intermediate microspheres and organized into finally multishell structures. The special microstructures actually recorded the evolution process of materials morphologies and microstructures in space and time scales, implying an intermediate-templating route, which is important for understanding and fabricating complex architectures. The Cu2O microspheres obtained were used to fabricate a gas sensor, which showed much higher sensitivity than solid C(u)2O microspheres.
506 citations
TL;DR: The compatibility of the room‐temperature process developed herein with commonly used plastic substrates may lead to applications such as the development of large‐area flexible solar cells.
Abstract: A new method for the preparation of active layers of polymeric solar cells without the need for thermal post-treatment to obtain optimal performance is presented. Poly(3-hexylthiophene) (P3HT) nanofibers are obtained in highly concentrated solutions, which enables the fabrication of nanostructured films on various substrates. Here, the preparation of these fibers along with their characterization in solution and in the solid state is detailed. By mixing these nanofibers with a molecular acceptor such as [6,6]-phenyl C61-butyric acid methyl ester (PCBM) in solution, it is possible to obtain in a simple process a highly efficient active layer for organic solar cells with a demonstrated power conversion efficiency (PCE) of up to 3.6 %. The compatibility of the room-temperature process developed herein with commonly used plastic substrates may lead to applications such as the development of large-area flexible solar cells.
TL;DR: In this article, a novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile and propylene as precursors, and Na-Y zeolite as a scaffold.
Abstract: A novel microporous templated carbon material doped with nitrogen is synthesized by using a two-step nanocasting process using acrylonitrile (AN) and propylene as precursors, and Na-Y zeolite as a scaffold. Liquid-phase impregnation and in situ polymerization of the nitrogenated precursor inside the nanochannels of the inorganic scaffold, followed by gas-phase impregnation with propylene, enables pore-size control and functionality tuning of the resulting carbon material. The material thereby obtained has a narrow pore-size distribution (PSD), within the micropore range, and a large amount of heteroatoms (i.e., oxygen and nitrogen). In addition, the carbon material inherits the ordered structure of the inorganic host. Such features simultaneously present in the carbon result in it being ideal for use as an electrode in a supercapacitor. Although presenting a moderately developed specific surface area (S BET =1680 m 2 g -1 ), the templated carbon material displays a large gravimetric capacitance (340 F g -1 ) in aqueous media because of the combined electrochemical activity of the heteroatoms and the accessible porosity. This material can operate at 1.2 V in an aqueous medium with good cycleability-beyond 10000 cycles-and is extremely promising for use in the development of high-energy-density supercapacitors.
TL;DR: In this paper, a mesoporous-nanotube hybrid composite, which consists of a thin layer of tetragonal tin dioxide with a disordered porous was embedded on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesophorous SnO2 on MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure-directing agents.
Abstract: A novel mesoporous-nanotube hybrid composite, namely mesoporous tin dioxide (SnO2) overlaying on the surface of multiwalled carbon nanotubes (MWCNTs), was prepared by a simple method that included in situ growth of mesoporous SnO2 on the surface of MWCNTs through hydrothermal method utilizing Cetyltrimethylammonium bromide (CTAB) as structure-directing agents. Nitrogen adsorption–desorption, X-ray diffraction and transmission electron microscopy analysis techniques were used to characterize the samples. It was observed that a thin layer tetragonal SnO2 with a disordered porous was embedded on the surface of MWCNTs, which resulted in the formation of a novel mesoporous-nanotube hybrid composite. On the base of TEM analysis of products from controlled experiment, a possible mechanism was proposed to explain the formation of the mesoporous-nanotube structure. The electrochemical properties of the samples as anode materials for lithium batteries were studied by cyclic voltammograms and Galvanostatic method. Results showed that the mesoporous-tube hybrid composites displayed higher capacity and better cycle performance in comparison with the mesoporous tin dioxide. It was concluded that such a large improvement of electrochemical performance within the hybrid composites may in general be related to mesoporous-tube structure that possess properties such as one-dimensional hollow structure, high-strength with flexibility, excellent electric conductivity and large surface area.
TL;DR: In this paper, the authors show that certain high rate capability olivines are distinguished by having extended lithium nonstoichiometry (up to ca. 20 %), with which is correlated a reduced lattice misfit as the material undergoes an electrochemically driven, reversible, first-order phase transformation.
Abstract: High energy lithium-ion batteries have improved performance in a wide variety of mobile electronic devices. A new goal in portable power is the achievement of safe and durable high-power batteries for applications such as power tools and electric vehicles. Towards this end, olivine-based positive electrodes are amongst the most important and technologically enabling materials. While certain lithium metal phosphate olivines have been shown to be promising, not all olivines demonstrate beneficial properties. The mechanisms allowing high power in these compounds have been extensively debated. Here we show that certain high rate capability olivines are distinguished by having extended lithium nonstoichiometry (up to ca. 20 %), with which is correlated a reduced lattice misfit as the material undergoes an electrochemically driven, reversible, first-order phase transformation. The rate capability in several other intercalation oxides can also be correlated with lattice strain, and suggests that nanomechanics plays an important and previously unrecognized role in determining battery performance.
TL;DR: In this paper, a polyaniline electrode was prepared by potentiostatic deposition of aniline on a hierarchically porous carbon monolith (HPCM), which was carbonized from the mesophase pitch.
Abstract: A high-performance polyaniline electrode was prepared by potentiostatic deposition of aniline on a hierarchically porous carbon monolith (HPCM), which was carbonized from the mesophase pitch. A capacitance value as high as 2200 F g–1 (per weight of polyaniline) is obtained at a power density of 0.47 kW kg–1 and an energy density of 300 W h kg–1. This active material deposited on HPCM also has the advantageous of high stability. These properties can be essentially attributed to the backbone role of HPCM. The method also has the advantage of a topology that is favorable for kinetics at high power densities, thus, contributing to the increase of ionic conductivity and power density. There is also no need for a binder, which not only lowers the preparation costs but also offers advantages in terms of stability and performance.
TL;DR: ZnO-SnO2 hollow spheres and hierarchical nanosheets were successfully synthesized using an aqueous solution containing ZnO rods, SnCl4, and NaOH by using a simple hydrothermal method as discussed by the authors.
Abstract: ZnO–SnO2 hollow spheres and hierarchical nanosheets are successfully synthesized using an aqueous solution containing ZnO rods, SnCl4, and NaOH by using a simple hydrothermal method. The effects of hydrothermal temperature and time on the morphology of ZnO–SnO2 are investigated. The formation process of ZnO–SnO2 hollow spheres and nanosheets is discussed. The samples are characterized using X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, and UV-vis absorption spectroscopy. Both hollow spheres and hierarchical nanosheets show higher photocatalytic activities in the degradation of methyl orange than that of ZnO rods or SnO2.
TL;DR: In this paper, a high-yield synthesis procedure is reported based on a cationic surfactant and low water content that additionally enables the adjustment of the size range of the individual particles between 50 and 100 nm.
Abstract: Nanometer-sized surfactant-templated materials are prepared in the form of stable suspensions of colloidal mesoporous silica (CMS) consisting of discrete, nonaggregated particles with dimensions smaller than 200 nm. A high-yield synthesis procedure is reported based on a cationic surfactant and low water content that additionally enables the adjustment of the size range of the individual particles between 50 and 100 nm. Particularly, the use of the base triethanolamine (TEA) and the specific reaction conditions result in long-lived suspensions. Dynamic light scattering reveals narrow particle size distributions in these suspensions. Smooth spherical particles with pores growing from the center to the periphery are observed by using transmission electron microscopy, suggesting a seed-growth mechanism. The template molecules could be extracted from the nanoscale mesoporous particles via sonication in acidic media. The resulting nanoparticles give rise to type IV adsorption isotherms revealing typical mesopores and additional textural porosity. High surface areas of over 1000 m 2 g -1 and large pore volumes of up to 1 mL g -1 are obtained for these extracted samples.
TL;DR: In this article, the evolution of nanomorphology within thin solid-state films of poly(3-alkylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3AT:PCBM) blends during the film formation and subsequent thermal annealing is reported.
Abstract: The evolution of nanomorphology within thin solid-state films of poly(3-alkylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3AT:PCBM) blends during the film formation and subsequent thermal annealing is reported. In detail, the influence of the P3AT's alkyl side chain length on the polymer/fullerene phase separation is discussed. Butyl, hexyl, octyl, decyl, and dodecyl side groups are investigated. All of the P3ATs used were regioregular. To elucidate the nanomorphology, atomic force microscopy (AFM), X-ray diffraction, and optical spectroscopy are applied. Furthermore, photovoltaic devices of each of the different P3ATs have been constructed, characterized, and correlated with the nanostructure of the blends. It is proposed that the thermal-annealing step, commonly applied to these P3AT:PCBM blend films, controls two main issues at the same time: a) the crystallization of P3AT and b) the phase separation and diffusion of PCBM. The results show that PCBM diffusion is the main limiting process for reaching high device performances.
TL;DR: In this paper, robust ultrathin multilayer films of silk fibroin were fabricated by spin coating and spin-assisted layer-by-layer assembly and their mechanical properties were studied both in tensile and compression modes for the first time.
Abstract: Robust ultrathin multilayer films of silk fibroin were fabricated by spin coating and spin-assisted layer-by-layer assembly and their mechanical properties were studied both in tensile and compression modes for the first time. The ultrathin films were characterized by a high elastic modulus of 6–8 GPa (after treatment with methanol) with the ultimate tensile strength reaching 100 MPa. The superior toughness is also many times higher than that usually observed for conventional polymer composites (328 kJ m–3 for the silk material studied here versus typical values of < 100 kJ m–3). These outstanding properties are suggested to be caused by the gradual development of the self-reinforcing microstructure of highly crystalline β-sheets, serving as reinforcing fillers and physical crosslinks, a process that is well known for bulk silk materials but it is demonstrated here to occur in ultrathin films as well, despite their limited dimensions. However, the confined state within films thinner than the lengths of the extended domains causes a significantly reduced elasticity which should be considered in the design of nanosized films from silk materials. Such regenerated silk fibroin films with outstanding mechanical strength have potential applications in microscale biodevices, biocompatible implants, and synthetic coatings for artificial skin.
TL;DR: LiTi2(PO4)3 as mentioned in this paper is a polyvinyl alcohol-assisted sol-gel-coated Nasicon-type phase LiMn2O4-based aqueous battery.
Abstract: Porous, highly crystalline Nasicon-type phase LiTi2(PO4)3 has been prepared by a novel poly(vinyl alcohol)-assisted sol–gel route and coated by a uniform and continuous nanometers-thick carbon thin film using chemical vapor deposition technology. The as-prepared LiTi2(PO4)3 exhibits excellent electrochemical performance both in organic and aqueous electrolytes, and especially shows good cycling stability in aqueous electrolytes. An aqueous lithium-ion battery consisting of a combination of LiMn2O4 cathode, LiTi2(PO4)3 anode, and a 1 M Li2SO4 electrolyte has been constructed. The cell delivers a capacity of 40 mA h g–1 and a specific energy of 60 W h kg–1 with an output voltage of 1.5 V based on the total weight of the active electrode materials. It also exhibits an excellent cycling stability with a capacity retention of 82 % over 200 charge/discharge cycles, which is much better than any aqueous lithium-ion battery reported.
TL;DR: It is demonstrated that, without further modification, plain electrospun fibers can help in peripheral nerve regeneration; however, the synergistic effect of an encapsulated growth factor facilitated a more significant recovery.
Abstract: Sustained release of proteins from aligned polymeric fibers holds great potential in tissue-engineering applications. These protein-polymer composite fibers possess high surface-area-to-volume ratios for cell attachment, and can provide biochemical and topographic cues to enhance tissue regeneration. Aligned biodegradable polymeric fibers that encapsulate human glial cell-derived neurotrophic factor (GDNF, 0.13 wt%) were fabricated via electrospinning a copolymer of caprolactone and ethyl ethylene phosphate (PCLEEP) with GDNF. The protein was randomly dispersed throughout the polymer matrix in aggregate form, and released in a sustained manner for up to two months. The efficacy of these composite fibers was tested in a rat model for peripheral nerve-injury treatment. Rats were divided into four groups, receiving either empty PCLEEP tubes (control); tubes with plain PCLEEP electrospun fibers aligned longitudinally (EF-L) or circumferentially (EF-C); or tubes with aligned GDNF-PCLEEP fibers (EF-L-GDNF). After three months, bridging of a 15 mm critical defect gap by the regenerated nerve was observed in all the rats that received nerve conduits with electrospun fibers, as opposed to 50% in the control group. Electrophysiological recovery was seen in 20%, 33%, and 44% of the rats in the EF-C, EF-L, and EF-L-GDNF groups respectively, whilst none was observed in the controls. This study has demonstrated that, without further modification, plain electrospun fibers can help in peripheral nerve regeneration; however, the synergistic effect of an encapsulated growth factor facilitated a more significant recovery. This study also demonstrated the novel use of electrospinning to incorporate biochemical and topographical cues into a single implant for in vivo tissue-engineering applications.
TL;DR: In this paper, a self-healing poly(dimethyl siloxane) elastomer is produced by the incorporation of a microencapsulated PDMS resin and a micro encapsulated crosslinker into the PDMS matrix.
Abstract: Self-healing functionality is imparted to a poly(dimethyl siloxane) (PDMS) elastomer. This new material is produced by the incorporation of a microencapsulated PDMS resin and a microencapsulated crosslinker into the PDMS matrix. A protocol based on the recovery of tear strength is introduced to assess the healing efficiency for these compliant polymers. While most PDMS elastomers possess some ability to re-mend through surface cohesion, the mechanism is generally insufficient to produce significant recovery of initial material strength under ambient conditions. Self-healing PDMS specimens, however, routinely recover between 70–100 % of the original tear strength. Moreover, the addition of microcapsules increases the tear strength of the PDMS. The effect of microcapsule concentration on healing efficiency is also investigated.
TL;DR: In this paper, the authors reported the high yield growth of monodispersed Cu 2 O nanocubes with approximate average sizes of 40, 65, 100, 230, and 420 nm using a seed-mediated synthesis approach.
Abstract: We report the high yield growth of monodispersed Cu 2 O nanocubes with approximate average sizes of 40, 65, 100, 230, and 420 nm using a seed-mediated synthesis approach in aqueous solution. The nanocubes are formed in 2 hours at room temperature. The standard deviation of the nanocube sizes in each sample is below 10 %. Structural analysis revealed that these nanocubes have six {100} faces, and possess truncated {110} edges and {111} corners. The combination of sodium dodecyl sulfate (SDS) and CuSO 4 was found to be critical to the formation of structurally well-defined Cu 2 O nanocubes. The nanocubes presumably were formed through the controlled aggregation of Cu 2 O seed particles and then surface reconstruction under the influence of SDS capping surfactant and sulfate ions to yield this truncated cubic structure. Optical characterization showed that nanocubes smaller than 100 nm absorb at -490 nm, while nanocubes larger than 200 nm display an absorption band at 515-525 nm. Additional absorption feature was observed in the red and near-infrared regions for the larger Cu 2 O nanocubes due to the light scattering effect. The investigation of the application of these nanocubes for the photodegradation of rhodamine B revealed the {111} crystal surfaces as the active surfaces responsible for the photocatalytic activity of Cu 2 O nanostructures. This simple and rapid synthesis of monodispersed Cu 2 O nanocubes should allow further examination of their various properties as a function of nanocrystal sizes.
TL;DR: In this paper, all-organic active matrix addressed displays based on electrochemical smart pixels made on flexible substrates are reported, where each individual smart pixel device combines an electrochemical transisto...
Abstract: All-organic active matrix addressed displays based on electrochemical smart pixels made on flexible substrates are reported. Each individual smart pixel device combines an electrochemical transisto ...
TL;DR: In this article, a comprehensive study of the origin of the low work function of nanostructured layers of Cs2CO3 prepared by solution deposition and thermal evaporation is presented.
Abstract: Nanostructured layers of Cs2CO3 are shown to function very effectively as cathodes in organic electronic devices because of their good electron-injection capabilities. Here, we report a comprehensive study of the origin of the low work function of nanostructured layers of Cs2CO3 prepared by solution deposition and thermal evaporation. The nanoscale Cs2CO3 layers are probed by various characterization methods including current–voltage (I–V) measurements, photovoltaic studies, X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), and impedance spectroscopy. It is found that thermally evaporated Cs2CO3 decomposes into CsO2 and cesium suboxides. The cesium suboxides dope CsO2, yielding a heavily doped n-type semiconductor with an intrinsically low work function. As a result, devices fabricated using thermally evaporated Cs2CO3 are relatively insensitive to the choice of the cathode metal. The reaction of thermally evaporated Cs2CO3 with Al can further reduce the work function to 2.1 eV by forming an Al–O–Cs complex. Solution-processed Cs2CO3 also reduces the work function of Au substrates from 5.1 to 3.5 eV. However, devices prepared using solution-processed Cs2CO3 exhibit high efficiency only if a reactive metal such as Al or Ca is used as the cathode metal. A strong chemical reaction occurs between spin-coated Cs2CO3 and thermally evaporated Al. An Al–O—Cs complex is formed as a result of this chemical reaction at the interface, and this layer significantly reduces the work function of the cathode. Finally, impedance spectroscopy results prove that this layer is highly conductive.
TL;DR: In this article, the pore characteristics and gas sorption properties of two microporous metal-organic framework structures, [M(bdc)(ted)0.5]·2DMF-0.2H 2 O (M=Zn (1), Cu (2); H2bdc=1,4-benzenedicarboxylic acid; ted=triethylenediamine; DMF: N,N-dimethylformamide) is reported.
Abstract: The design, synthesis, and structural characterization of two microporous metal-organic framework structures, [M(bdc)(ted)0.5]·2DMF-0.2H 2 O (M=Zn (1), Cu (2); H2bdc=1,4-benzenedicarboxylic acid; ted=triethylenediamine; DMF: N,N-dimethylformamide) is reported. The pore characteristics and gas sorption properties of these compounds are investigated at cryogenic temperatures, room temperature, and higher temperatures by experimentally measuring argon, hydrogen, and selected hydrocarbon adsorption/desorption isotherms. These studies show that both compounds are highly porous with a pore volume of 0.65 (1) and 0.52 cm 3 g -1 (2). The amount of the hydrogen uptake, 2.1 wt % (1) and 1.8 wt % (2) at 77 K (1 atm; 1 atm =101 325 Pa), places them among the group of metal-organic frameworks (MOFs) having the highest H 2 sorption capacity. [Zn(bdc)(ted) 0.5 ]·2 DMF·0.2 H 2 O adsorbs a very large amount of hydrocarbons, including methanol, ethanol, dimethylether (DME), n-hexane, cyclohexane, and benzene, giving the highest sorption values among all metal-organic based porous materials reported to date. In addition, these materials hold great promise for gas separation.
TL;DR: Overall, this work demonstrates that the properties of HA nanocrystals can be modulated in such a way to produce HA/biomolecule conjugates tailored for specific therapeutic applications.
Abstract: This Full Paper investigates the adsorption and desorption of the anticancer drugs cis-diamminedichloroplatinum(II) (CDDP, cisplatin) and the new platinum(II) complex di(ethylenediamineplatinum)medronate (DPM), as well as the clinically relevant bisphosphonate alendronate, towards two biomimetic synthetic HA nanocrystalline materials with either plate-shaped (HAps) or needle-shaped (HAns) morphologies and different chemico-physical properties. The adsorption and desorption kinetics are dependent on the specific properties of the drugs and the morphology of the HA nanoparticles. Adsorption of the platinum complexes occurs with retention of the nitrogen ligands but the chloride ligands of cisplatin are displaced. Despite their opposite charges, the negatively charged alendronate bisphosphonate and the positively charged aquated cisplatin are strongly adsorbed, while the neutral DPM complex shows lower affinity towards the negatively charged apatitic surface. The data suggest that adsorption of the two platinum complexes is driven by electrostatic attractions, while interaction between the alendronate and the HA surface takes place by ligand exchange in which the two phosphonate groups of the drug molecule replace two surface phosphate groups. Significantly, adsorption of positively charged hydrolysis species of cisplatin is more favored on the phosphate-rich HAns surface while adsorption of negatively charged alendronate is more favored on the calcium-rich HAps surface. The latter type of short-range electrostatic interactions also appear to dominate the desorption kinetics; consequently, drug release is greater for neutral DPM than for charged alendronate and aquated cisplatin. Moreover, while the release per unit area of charged species is the same for the two types of HAs, the release of DPM is faster from HAns, which is lower in surface calcium, than for HAps. Overall, this work demonstrates that the properties of HA nanocrystals can be modulated in such a way to produce HA/biomolecule conjugates tailored for specific therapeutic applications.
TL;DR: A metal-semiconductor-metal (M-S-M) model for quantitative analysis of currentvoltage (I-V) characteristics of semiconducting nanowires is described and applied to fit experimental I-V curves of Bi2S3 nanowire transistors as mentioned in this paper.
Abstract: A metal-semiconductor-metal (M-S-M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi2S3 nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M-S-M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi2S3 nanowires and compared with the field-effect based method.
TL;DR: The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors.
Abstract: Light emitting field effect transistors based on molecular and polymeric organic semiconductors are multifunctional devices that integrate light emission with the current modulating function of a transistor. The planar geometry of organic light emitting field effect transistors (OLEFETs) offers direct access to the light emission region, providing a unique experimental configuration to investigate fundamental optical and electronic properties in organic semiconductors. OLEFETs show great potential for technological applications such as active matrix full color electroluminescent displays. In this Feature Article we review advances in OLEFETs since their first demonstration in 2003 and we highlight exciting challenges associated with their future development.
TL;DR: In this paper, two metallic inkjet-printable materials are studied: i) a silver-copper nanoparticle based dispersion and ii) a soluble organic silver-precursor.
Abstract: The field of organic electronics has seen tremendous progress over the last years and all-solution-based processes are believed to be one of the key routes to ultra low-cost roll-to-roll device and circuit fabrication. In this regard a variety of functional materials has been successfully designed for inkjet printing. While orthogonal-solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field-effect transistors (OFET) and their curing concepts. Two metallic inkjet-printable materials are studied: i) a silver-copper nanoparticle based dispersion and ii) a soluble organic silver-precursor. Photoelectron spectroscopy reveals largely metallic properties of the cured materials, which are compared with respect to OFET performance and process-related issues. Contact resistance of the prepared metal electrodes is significantly larger than that of evaporated top-contact gold electrodes. As direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 μm, the influence of contact resistance is rather small, however, and overall device performance is comparable.