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Magnetic bearing is an important part of modern high-speed rotating machinery. The performance of power electronic converter highly determines the quality of magnetic bearing drive. In this paper, a fault-tolerant converter with series-winding topology is introduced. Compared with the traditional topology, the current stress of the phase leg is reduced while the utilization of DC voltage is guaranteed, and fault-tolerant operation can be realized in the case of open circuit fault of the switching device. This paper introduces the characteristics of the series-winding topology and the current control method. Open circuit fault detection methods and countermeasures are also analyzed. Experimental results show the effectiveness of the proposed topology. Fault-tolerant experiments under static suspension and rotation of the rotor demonstrate the performance of the topology. This kind of series-winding topology provides a new scheme with good performance and high reliability for the design of magnetic bearing controllers.

Conjugated polymer extraction (CPE)-enriched high-purity semiconducting (sc) single-walled carbon nanotubes (SWCNTs) have demonstrated significant application potential as emerging electronic materials. In this work, the interaction of three fluorene-based copolymers with sc-SWCNTs in a toluene solution was systematically compared, covering a wide range of concentrations while considering the phase behavior of the polymer itself. 2D photoluminescence excitation studies show that the polymer containing semiconjugated pyridine units had a higher binding affinity to the SWCNTs due to its twistable main chain conformation. The uniform and high-density SWCNT networks deposited on a silicon wafer have been characterized by SEM and spatial Raman spectroscopy, which reveals ultrahigh sc purity with a metallic tube content less than the parts per million level. The performance of thin-film transistors could be correlated with the structure of wrapping polymers. The threshold voltage shifted with the nitrogen content in their repeat units due to electron donation from the nitrogen atoms. The off-current was reduced with the flexible copolymer, which provided better wrapping and thus limited bundling during network formation.

SWCNT-based thin-film transistors (TFTs) typically display unipolar p-type electrical characteristics in ambient condition due to the O₂/H₂O redox couple. However, complementary circuits that combine both p and n channels are preferred due to lower power requirements. Typical approaches with small molecule or polymeric dopants often yield ambipolar devices, or unstable n-type devices while concomitantly suppressing the on-current and mobility. Herein, we demonstrate a charge carrier control strategy using aqueous-based polymeric coatings that enable n-type devices with comparable performance to p-type devices. Specifically, we used a polyvinyl alcohol (PVA) coating layer containing a minority fraction of polyethyleneimine (PEI) (0.06–1.1 % w/w) to effectively switch the transfer characteristics from p-type to n-type, while maintaining decent electrical characteristics. Moreover, we demonstrate the ability to fine-tune the n branch threshold voltage via the annealing temperature. A similar strategy provides a balanced p branch on-current by incorporating PVA as a minor component (0.1-6 % w/w) into a polyacrylic acid (PAA) matrix. Through effective n-type conversion and p-type balancing, we demonstrate a simple SWCNT-based inverter. Considering the low-cost, environmentally friendly compositions and aqueous processability, this approach is attractive for large scale complementary printable circuits.

This paper sets up a one-sector endogenous growth model to evaluate the impact of maintenance policy on a decentralized economy. It analyzes how the maintenance policy and the nonlinear and endogenous depreciation of private capital facilitate the household’s optimistic expectation to realize. It is shown that the role of the accelerated depreciation of private capital is the key to generate local indeterminacy regardless of the tax financing regime. These theoretical findings with respect to the linkage between local indeterminacy and public maintenance are not common in the existing literature. In addition, our findings also have some important policy implications. The public sector should prudently assess the situations of private capital depreciation to reduce the occurrence of local indeterminacy while adopting the maintenance policy.

Challenges frequently faced during the analysis of selenomethionine in complex matrices such as food and environmental samples include the lack of SI-traceable primary standards as well as difficulties associated with complex sample preparation methods resulting in potentially biased measurement results. In an effort to overcome these challenges, the National Research Council Canada has prepared two selenomethionine reference materials: a high-purity powder of natural isotopic abundance (SENS-1), and a solution of selenium-82 labelled selenomethionine (SEES-1). The purity of SENS-1, 0.961 ± 0.007 g g−1 (k = 2), was established through quantitative nuclear magnetic resonance spectroscopy combined with data from inductively-coupled plasma mass spectrometry for total selenium content and the HPLC analysis of selenium-containing impurities. With the chemical purity of SENS-1 established, it was then used as the primary standard for reverse isotope dilution analysis, where the concentration of selenomethionine in SEES-1 was determined to be 1556 ± 60 μg g−1 (k = 2).

High-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs) are promising for portable and high-sensitivity gas sensors because of their excellent physical and electrical properties. Here, we describe the synthesis of a novel indigo-fluorene-based copolymer (PFIDBoc) that has been designed to selectively enrich sc-SWCNTs with excellent purity (>99.9%) yet contain a latent function in the form of a tert-butoxy (t-BOC)-protected amine that can be later revealed and exploited for carbon dioxide (CO₂) gas sensing. SWCNTs wrapped with the PFIDBoc polymer can be easily converted via an on-chip thermal process to reveal a vinylogous amide moiety with a secondary amine nitrogen within the indigo building block of the copolymer which is perfectly suited for CO₂ recognition. Thin-film transistors and sensors were inkjet-printed onto rigid and flexible substrates, demonstrating the versatility of enriched PFIDBoc-derived sc-SWCNT dispersions. The printed transistors exhibited a mobility up to 9 cm² V⁻¹ s⁻¹ and on/off current ratios >10⁵. We further demonstrate herein a CO₂ sensor for indoor air quality monitoring even in low humidity environments, possessing a linear response with up to ∼5.4% sensitivity and a dynamic range between 400 and 2000 ppm in air with a relative humidity of ∼ 40%.

Nanomaterials are ideal for electrochemical biosensors, with their nanoscale dimensions enabling the sensitive probing of biomolecular interactions. In this study, we compare field-effect transistors (FET) comprised of unsorted (un-) and semiconducting-enriched (sc-) single-walled carbon nanotubes (SWCNTs). un-SWCNTs have both metallic and semiconducting SWCNTs in the ensemble, while sc-SWCNTs have a >99.9% purity of semiconducting nanotubes. Both SWCNT FET devices were decorated with gold nanoparticles (AuNPs) and were then employed in investigating the Ca2+-induced conformational change of calmodulin (CaM) - a vital process in calcium signal transduction in the human body. Different biosensing behavior was observed from FET characteristics of the two types of SWCNTs, with sc-SWCNT FET devices displaying better sensing performance with a dynamic range from 10-15 M to 10-13 M Ca2+, and a lower limit of detection at 10-15 M Ca2+.

The development of printable and air-stable unipolar n-type semiconductors remains a critical issue in the field of organic electronics in view of n-type transistors being indispensable components in the manufacture of low-power-consumption complementary (CMOS type) integrated circuits. In this work, we report on two dicyanomethylene-substituted diketopyrrolopyrrole derivatives with different alkyl side chains (DCM-DPP-C13 and DCM-DPP-C16) for n-type transistors. Compared with DCM-DPP-C16, the side chain branching point in DCM-DPP-C13 was moved further away from the conjugated backbone. Both materials showed promising electron mobility above 0.1 cm2/VS in air with remarkably low threshold voltages (−3 V – 2 V) on spin-coated bottom-contact bottom-gated devices on silicon substrates. Contrary to our original expectation, the average electron mobility of DCM-DPP-C16 (0.2 cm2/VS) was higher than that of DCM-DPP-C13 (0.12 cm2/VS) due to the bigger crystalline domains in the thin film of the former compound. We investigated the inkjet printability of these two compounds as well, and bottom-contact top-gated transistors were successfully fabricated on flexible PET substrates. Widely used Cytop was employed as the gate dielectric. Ag gate electrodes were readily inkjet printed on the gate dielectric by using a thin layer of Nafion as an adhesion promoter. DCM-DPP-C16 demonstrated an excellent inkjet-ability with good uniformity and reproducibility. An average electron mobility around 0.1 cm2/VS was achieved in air. This is an important step toward the fabrication of large-area organic CMOS logic circuits with low cost.

The high sensitivity of carbon nanotube devices as gas sensors is generally attributed to the large surface area of the material, whereas selectivity is often imparted by the “lock-and-key” mechanism. In contrast with this picture, where little function is conferred to the underlying substrate, we demonstrate that bottom gate carbon nanotube network field-effect transistors (CNN-FETs) fabricated on a variety of polymer dielectrics, but with the same pristine carbon nanotubes, show differentiated responses to analytes. Interaction with the environment thus occurs not only directly with carbon nanotubes but is often mediated by the substrate. In a broad survey of polymers, we identify several materials suitable as the gate dielectric of printed devices and that yield a vanishing gate hysteresis in ambient air. The other two classes of polymers that induce a lagging or advancing hysteresis in CNN-FETs are found desirable for gas sensing applications. Moreover, we have tested CNN-FETs with different polymer gate dielectrics against a series of analytes ranging from common alcohols to organic solvents and amines, among others. A rich set of distinct and complementary analyte signatures could be observed, identifying the polymer gate dielectric as a differentiator for chemical discrimination in a future printed cross-reactive sensor array, that is, an electronic nose.

Active Magnetic Bearing (AMB) has been widely applied in occasions acquire high-speed rotating, high-precision machining, and so on. The AMB can provide active control force to offset centrifugal force and other disturbance to suppress vibration while rotating. This paper proposed a strategy to compensate vibration in AMB system based on Variable Step-size Automatic Learning Control (VALC). Firstly, a two degrees of freedom model of radial AMB is established. Phase error between of centrifugal force and synchronous vibration is analyzed. Then, principle and process of VALC is introduced. A generalized notch filter is applied to obtain synchronous and harmonic vibration. Next, simulations are carried out based on AMB control system applied VALC. The results of simulations show the feasibility of the compensating strategy. Experiments to reduce synchronous and harmonic vibration based on VALC are carried out on a test rig. Spectrums of vibration signals show that vibration is reduced by about 90%, which demonstrates the effectiveness of proposed strategy for vibration compensation.

Although carbon nanotube transistors present outstanding performances based on key metrics, large-scale uniformity and repeatability required in printable electronics depend greatly on proper control of the electrostatic environment. Through a survey of polymer dielectric encapsulants compatible with printing processes, a simple correlation is found between the measured interfacial charge density and the onset of conduction in a transistor, providing a rational route to control the electrical characteristics of carbon nanotube transistors. Smooth and continuous balancing of the properties between unipolar p-type and n-type transport is achieved using a molar fraction series of poly(styrene-co-2-vinylpyridine) statistical copolymers combined with an electron-donating molecule. We further demonstrate the easy fabrication of a p-n diode which shows a modest rectification of 8:1.

We describe a technique to prepare ensembles of neat, unbundled single-walled carbon nanotubes decorated with pure size-filtered metal nanoparticles. Polymer-encased nanotubes are drop-cast on nanoporous transmission electron microscope membrane grids, mounted within a nanoparticle-deposition apparatus, baked in situ to remove the polymer coating, and exposed to a beam of pure size-selected metal nanoparticles. Subsequent electron microscopy imaging reveals the presence of nanoparticles supported by pure suspended single-walled nanotubes. This method is promising for efficient production of prototype chemical and physical devices which require the presence of clean well-defined nanoparticle-nanotube hybrids for characterization, imaging, and applications.

Conjugated polymer extraction (CPE) is a low-cost, scalable process that can enrich single-walled carbon nanotube (SWCNT) materials in organic media. For other separation methods in aqueous phases, redox chemistry and/or pH control dramatically affect the sorting process of the SWCNTs. We have previously determined that the CPE process can be fine-tuned by adjusting the pH on the tube surface. Here, we systematically studied the effect of redox chemistry on the CPE process by adding organic p-/n-dopants. At a very strong p-/n-doping level, static repulsions dominated the interactions between the tubes and the CPE lost selectivity. When the doping level changed from a medium p-doping to a neutral state, the yield of CPE increased and the selectivity was compromised. We also observed chiral selectivity when a weak p-dopant was used. A photoluminescence excitation mapping under different titration conditions provided more insight into the doping level of the tubes relative to their diameters, chiralities, and redox potentials. We proposed a mechanism for the CPE process. The semiconducting and metallic tubes are separated because of their different solubilities, which are determined by the bundling energy between the tubes and are related to their doping level in polymer solutions.

Conjugated polymer extraction (CPE) has been shown to be a highly effective method to isolate high-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs). In both literature reports and industrial manufacturing, this method has enabled enrichment of sc-SWCNTs with high purity (≥99.9%). High selectivity is typically obtained in nonpolar aromatic solvents, yet polar solvents may provide process improvements in terms of yield, purity and efficiency. Using an amphiphilic fluorene-alt-pyridine conjugated copolymer with hydrophilic side chains, we have investigated the enrichment of sc-SWCNTs in polar solvents. Various conditions such as polymer/SWCNT ratio, solvent polarity, solvent dielectric constant as well as polymer solubility and SWCNT dispersibility were explored in order to optimize the purity and yield of the enriched product. Herein, we provide insights on CPE by demonstrating that a conjugated polymer having a hydrophobic backbone and hydrophilic oligo(ethylene oxide) side chains provides near full recovery (95%) of sc-SWCNTs using a multiextraction protocol. High purity is also obtained, and differences in chiral selectivity compared to analogous hydrophobic systems were confirmed by optical absorption and Raman spectroscopy as well as photoluminescence excitation mapping. Taking into consideration the solvent dielectric constant, polarity index as well as polymer solubility and SWCNT dispersibility provides a better understanding of structure–property effects on sc-SWCNT enrichment. The resulting hydrophilic SWCNT dispersions demonstrate long-term colloidal stability, making them suitable for ink formulation and high-performance thin-film transistors fabrication.

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are emerging as a promising material for high-performance, high-density devices as well as low-cost, large-area macroelectronics produced via additive manufacturing methods such as roll-to-roll printing. Proof-of-concept demonstrations have indicated the potential of sc-SWCNTs for digital electronics, radiofrequency circuits, radiation hard memory, improved sensors, and flexible, stretchable, conformable electronics. Advances toward commercial applications bring numerous opportunities in SWCNT materials development and characterization as well as fabrication processes and printing technologies. Commercialization in electronics will require large quantities of sc-SWCNTs, and the challenge for materials science is the development of scalable synthesis, purification, and enrichment methods. While a few synthesis routes have shown promising results in making near-monochiral SWCNTs, gram quantities are available only for small-diameter sc-SWCNTs, which underperform in transistors. Most synthesis routes yield mixtures of SWCNTs, typically 30% metallic and 70% semiconducting, necessitating the extraction of sc-SWCNTs from their metallic counterparts in high purity using scalable postsynthetic methods. Numerous routes to obtain high-purity sc-SWCNTs from raw soot have been developed, including density-gradient ultracentrifugation, chromatography, aqueous two-phase extraction, and selective DNA or polymer wrapping. By these methods (termed sorting or enrichment),99% sc-SWCNT content can be achieved. Currently, all of these approaches have drawbacks and limitations with respect to electronics applications, such as excessive dilution, expensive consumables, and high ionic impurity content. Excess amount of dispersant is a common challenge that hinders direct inclusion of sc-SWCNTs into electronic devices. At present, conjugated polymer extraction may represent the most practical route to sc-SWCNTs. By the use of polymers with a π-conjugated backbone, sc-SWCNTs with99.9% purity can be dispersed in organic solvents via a simple sonication and centrifugation process. With 1000 times less excipient and the flexibility to accommodate a broad range of solvents via diverse polymer constructs, inks are readily deployable in solution-based fabrication processes such as aerosol spray, inkjet, and gravure. Further gains in sc-SWCNT purity, among other attributes, are possible with a better understanding of the structure-property relationships that govern conjugated polymer extraction. This Account covers three interlinked topics in SWCNT electronics: metrology, enrichment, and SWCNT transistors fabricated via solution processes. First, we describe how spectroscopic techniques such as optical absorption, fluorescence, and Raman spectroscopy are applied for sc-SWCNT purity assessment. Stringent requirements for sc-SWCNTs in electronics are pushing the techniques to new levels while serving as an important driver toward the development of quantitative metrology. Next, we highlight recent progress in understanding the sc-SWCNT enrichment process using conjugated polymers, with special consideration given to the effect of doping on the mechanism. Finally, developments in sc-SWCNT-based electronics are described, with emphasis on the performance of transistors utilizing random networks of sc-SWCNTs as the semiconducting channel material. Challenges and advances associated with using polymer-based dielectrics in the unique context of sc-SWCNT transistors are presented. Such transistor packages have enabled the realization of fully printed transistors as well as transparent and even stretchable transistors as a result of the unique and excellent electrical and mechanical properties of sc-SWCNTs.

Nanomaterials are ideal for electrochemical biosensors, with their nanoscale dimensions enabling the sensitive probing of biomolecular interactions. In this study, we compare field-effect transistors (FET) comprised of unsorted (un-) and semiconducting-enriched (sc-) single-walled carbon nanotubes (SWCNTs). un-SWCNTs have both metallic and semiconducting SWCNTs in the ensemble, while sc-SWCNTs have a99.9% purity of semiconducting nanotubes. Both SWCNT FET devices were decorated with gold nanoparticles (AuNPs) and were then employed in investigating the Ca

Enrichment schemes providing high-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs) will enable their implementation into high end and printed electronics. Conjugated polymer extraction (CPE) has been shown to be a very effective and scalable method to isolate sc-SWCNTs with purities >99.9%. However, this method is often plagued with variability, and the mechanism is not thoroughly understood. Herein, we probe the origins of selectivity in polyfluorene-assisted enrichment using poly(9,9-di-n-dodecylfluorene) (PFDD) and find that the affinity of the wrapping polymer to bind metallic (m-) and semiconducting SWCNTs is similar and may not contribute to the selectivity, but rather that oxygen-driven p-doping of the nanotubes and its dependence on the surface acidity may play a vital role for the selective dispersion of sc-SWCNT. The latter hypothesis is tested by titration experiments in which sodium hydroxide (NaOH) is used to neutralize the SWCNT surface, thus mitigating oxygen p-doping of SWC...

In this study, we report the characterization of three arsenobetaine-certified reference materials by quantitative NMR. We have synthesized an arsenobetaine bromide high-purity standard of natural isotopic composition (ABET-1) and two carbon-13-labeled isotopic standards (BBET-1 and CBET-1). Assignments of the chemical purity and isotopic composition are not trivial in the case of arsenobetaine, and in this study we utilized quantitative(1)H-NMR techniques for the determination of the mass fractions (chemical purity). The isotopic purity of all three standards was also assessed by NMR from the carbon-13 satellite signals. The standards are non-hygroscopic, high-purity (ca. 0.99 g/g), and the carbon-13 enrichment for both isotopic standards is x((13)C)≈0.99. These standards are designed for use as primary calibrators for mass spectrometric determination of arsenobetaine in environmental samples.

Author(s): Sun, J; Sapkota, A; Park, H; Wesley, P; Jung, Y; Maskey, BB; Kim, Y; Majima, Y; Ding, J; Ouyang, J; Guo, C; Lefebvre, J; Li, Z; Malenfant, PRL; Javey, A; Cho, G | Abstract: A limitless-length flexible active-matrix implies that virtually any surface can be rendered into an interactive medium when laminated with electrophoretic or organic light-emitting diode sheets. However, performance, cost, and size limitations of current fabrication technologies and semiconducting materials, typically utilized in thin film transistor (TFT) active matrices (TFT-AMs), have hindered progress, thus preventing the realization of fully printed TFT-AMs on a plastic roll. A new high-purity semiconducting single-walled carbon nanotube (s-SWCNT) ink is prepared by first isolating 99.9% pure s-SWCNTs via conjugated polymer extraction, and then utilizing a ligand-exchange method to formulate a novel hydrophilic gravure-compatible semiconducting ink. Based on the s-SWCNT ink, a fully additive manufacturing process using roll-to-roll (R2R) gravure printing enables the fabrication of a flexible TFT-AM, overcoming performance, cost, and size limitations. TFT-AMs with 10 to 40 PPI resolution where average mobility of 0.23 ± 0.12 cm2 V−1 s−1, average on–off ratio of 104.1, and threshold voltage variation of ±13% are attained. As a proof of concept, an inexpensive and flexible electrophoretic display is demonstrated by simply laminating an electrophoretic sheet onto the R2R gravure-printed s-SWCNT-based TFT-AM.

Bulk heterojunction (BHJ) organic solar cells based on p-type polymers and n-type fullerene derivatives have attracted increasing attention due to their promising potential for providing low–cost solar electricity. In this paper, we will introduce our recent work on the development of new fullerene derivatives. Through Rh complex catalyzed coupling reactions and cycloaddition reactions, we attached several organic functional groups to the fullerene skeleton. It was found that the organic substituents had little impact on the fullerene energy levels. Instead, the organic substituents have huge impact on the other physical properties of the resulting fullerene derivatives, such as solubility, crystallinity, and electron mobility. We designed and synthesized a novel series of alkoxy substituted indene derivatives as solubilizing groups for fullerenes. Preliminary experimental results demonstrated that these 5-alkoxyindene modified C70 derivatives are superior to widely used PC71BM when blended with poly[N-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'- benzothiadiazole)](PCDTBT) in BHJ solar cells. The device series resistance decreased from 10 cm2 for the PC71BM based device to 4 cm2 for the 5-methoxyindene-C70 monoadduct based device. As a result, the device fill factor increased from 0.60 to 0.69, and the overall EQE-calibrated power conversion efficiency was enhanced from 5.6% to 6.2%., International Conference on Renewable Energies and Power Quality (ICREPQ’18), March 21-23, 2018, Salamanca, Spain

The purity of single-wall carbon nanotube (SWCNT) ensembles is critical, but assessing the purity in terms of metal vs semiconductor content is challenging at high purities. We describe possible bulk Raman spectroscopy based procedures to assess this metallicity and compare it to absorption procedures. A simple metric for metallicity is the G+ band peak intensity ratio at two appropriate wavelengths. Related metallic G– band area derived metrics extend to higher purities. The G band signal scales linearly over orders of magnitude in concentration. However, the ratio-derived metrics may still be nonlinear because of resonance. Therefore, they break down if the tube diameter distributions differ greatly between samples, and other complications are possible. Additionally, the absolute Raman cross sections for each type of SWCNT can be estimated, and the abundance of semiconductors and metals can be tracked independently. Raman-derived metallicity figures of merit can meaningfully evaluate samples of purities which are not otherwise easily accessible, but there are important limitations to this simple approach to metallicity assessment.

Cyanocobalamin (CNCbl) is an active form of vitamin B12, commonly employed for the preparation of multivitamin supplements and fortified food. In this study, we present a novel analytical method for its determination based on stable isotope dilution liquid chromatography electrospray tandem mass spectrometry (ID LC-MS/MS). Isotopically enriched 13C15NCbl was synthesized in-house and used as internal standard. The method was validated using NIST SRM 3280 multivitamin reference material and by comparison with an independent methodology based on LC-ICPMS. The proposed method provided a detection limit of 57 pg/g and could be applied for the determination of trace level of CNCbl in multivitamin supplements with a relative standard uncertainty better than 3%. The novel ID LC-MS/MS is a primary ratio method that could become a reference for CNCbl determination in multivitamins and food supplements. The method was applied for the characterization of two NRC multivitamin tablet Certified Reference Material (CRM) candidates, VITA-1 and VITB-1 whose CNCbl levels were quantified as 2.64 ± 0.09 and 1.75 ± 0.12 μg/g, respectively.

In this work, a modification to the captive bubble method was proposed to test the advancing and receding contact angle. This modification is done by adding a pressure chamber with a pressure control system to the original experimental system equipped with an optical angle mater equipped with a high speed CCD camera, a temperature control system and a computer. A series of samples with highly hydrophilic, hydrophilic, hydrophobic and superhydrophobic surfaces were prepared. The advancing and receding contact angles of these samples with highly hydrophilic, hydrophilic, and hydrophobic surfaces through the new methods was comparable to the result tested by the traditional sessile drop method. It is proved that this method overcomes the limitation of the traditional captive bubble method and the modified captive bubble method allows a smaller error from the test. However, due to the nature of the captive bubble technique, this method is also only suitable for testing the surface with advancing or receding contact angle below 130°. © 2014 Elsevier B.V. All rights reserved.

Increasing use of single-walled carbon nanotubes (SWCNTs) necessitates a novel method for hazard risk assessment. In this work, we investigated the interaction of several types of commercial SWCNTs with single-stranded (ss) and double-stranded (ds) DNA oligonucleotides (20-mer and 20 bp). Based on the results achieved, we proposed a novel assay that employed the DNA interaction potency to assess the hazard risk of SWCNTs. It was found that SWCNTs in different sizes or different batches of the same product number of SWCNTs showed dramatically different potency of interaction with DNAs. In addition, the same SWCNTs also exerted strikingly different interaction potency with ss- versus ds- DNAs. The interaction rates of SWCNTs with DNAs were investigated, which could be utilized as the indicator of potential hazard for acute exposure. Compared to solid SWCNTs, the SWCNTs dispersed in liquid medium (2% sodium cholate solution) exhibited dramatically different interaction potency with DNAs. This indicates that the exposure medium may greatly influence the subsequent toxicity and hazard risk produced by SWCNTs. Based on the findings of dose-dependences and time-dependences from the interactions between SWCNTs and DNAs, a new chemistry based assay for hazard risk assessment of nanomaterials including SWCNTs has been presented.

A simple and low-cost technique for the preparation of silicon-oil-infused polydimethylsiloxane (PDMS) coatings with different silicon oil contents have been developed and studied. This material is designed for ice-phobic applications, and thus a high hydrophobic property of PDMS is maintained by avoiding any polar groups such as C=O and OH in the structure. Therefore, the polymer main chain was attached with vinyl and Si-H groups to obtain a cross-linking capability, meanwhile to ensure a nonpolar chemical structure. Its ice-phobic property has been investigated in terms of ice adhesion strength (tensile and shear), water contact angle, icing dynamics using high-speed photography and morphology using TEM, SEM and AFM. The prepared coating surface shows a low surface energy and very low ice adhesion strength of 50 kPa, only about 3% of the value on a bare aluminum (Al) surface. In the silicon oil infused PDMS coatings, the low surface energy of the silicon oil and PDMS, and the high mobility of silicon oil played an important role on the ice-phobic property. Both of these factors offer the surface a large water contact angle and hence a small contact area, leading to the formation of a loose ice layer. In addition, the oil infused polymer structure significantly reduces the contact area of the ice with solid substrate since the ice mostly contacts with the mobile oil. This leads to a very weak interaction between the substrate and ice, consequently significantly reduces the ice adhesion strength on the surface. Therefore, such material could be a good candidate for ice-phobic coatings on which the accumulated ice may be easily removed by a nature force, such as wind, gravity, and vibration. © 2013 American Chemical Society.

Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at -10 C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30 under an extremely condensing weather condition (-10 C and relative humidity of 85-90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surface after the surface was undergone 20 icing/ice-breaking cycles and 40 icing/ice-melting cycles, respectively. Surface profile and XPS studies on these surfaces indicated a minor damage of the surface nano/microstructure and the coating layer upon these multiple ice-breaking and ice-melting processes. Therefore, this superhydrophobic surface could be a good candidate for icephobic applications. © 2013 American Chemical Society.

The synthesis of a new alternating conjugated polymer, PDTTTPD, based on electron-donating dithieno[3,2-b:2′,3′-d]thiophene (DTT) and electron-withdrawing thieno[3,4-c]pyrrole-4,6-dione (TPD) units is reported. This polymer shows strong thermochromic effect in chlorobenzene with a peak shift up to 170 nm. This phenomenon is studied with fluorescence spectroscopy and related to the steric hindrance along the polymer main chain. Polymer solar cells are fabricated from its blends with PC71BM, and shows modest power conversion efficiency up to 2.1%. The low efficiency is due to the low short-circuit current, which is also attributed to the steric effect. Based on these results, a general design rule for polymer photovoltaic material with controlled backbone conformation is proposed. A new alternating conjugated polymer, PDTTTPD, based on electron-rich dithieno[3,2-b:2′,3′-d] thiophene (DTT) and electron-deficient thieno[3,4-c]pyrrole-4,6-dione (TPD) building blocks is designed and synthesized. PDTTTPD shows strong thermochromic effect in chlorobenzene solution and modest PCE of 2.1% in organic solar cell devices due to the steric hindrance induced twisting of the conjugated main chain. A general design rule is then suggested to control the main chain conformation of polymer materials for photovoltaic applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Polymer/inorganic-nanocrystals bulk heterojunction solar cells, where inorganic semiconductor nanocrystals such as CdSe, CdS, CdTe, ZnO, TiO 2 , and silicon, replace the fullerene molecules as the electron acceptors, typically exhibit a power conversion efficiency (PCE) below 3% even after tremendous engineering efforts to optimize the nanocrystal size, shape, and nanoscale morphology. One promising feature of polymer hybrid solar cells is the ability to sensitize conjugated polymers, which on their own absorb only in the visible part of solar spectrum, into the infrared spectral range using infrared-active lead salt nanocrystal quantum dots (NQDs). Here we observed for the first time hole transfer from PbS NQDs to polymers as evidenced by the quenching of the PbS photoluminescence (PL), a sign of the presence of charge separating type II heterojunction. The type II band-offset at the NQD/polymer heterojunction enables efficient hole extraction from NQDs and leads to a record PCE of 3.80%, realized in a planar junction configuration under simulated air mass 1.5 global (AM 1.5G) irradiation of 100 mW/cm 2 . The photocurrent has an extended spectral range spanning from the ultraviolet (UV) to the infrared (IR). Contributions from the polymer and PbS to the photocurrent were identified. Infrared photons (>700 nm) contribute about 30% of the photocurrent and yield a high external quantum efficiency (EQE) of 20% at 1050 nm.

In this work, we have fabricated superhydrophobic aluminum surfaces by a facile chemical etching method. Surface morphology and composition were studied by using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). To comparatively investigate the effect of environmental factors on superhydrophobic behaviors of surfaces with different low-surface-energy coatings under controllable condensation conditions, contact and sliding angles were measured from −10 °C to 30 °C under relative humidity (RH) of 30, 60 and 90%, respectively. The calculation of the solid–liquid contact area fraction quantitatively explained the increased wettability characterized by descending contact angle and ascending sliding angle under low temperature and high humidity, and indicated a transition of the equilibrium state from Cassie–Baxter to Wenzel on rough surfaces. The wettability restoration test showed that the loss of superhydrophobicity during condensation could be recovered completely after a drying process at room temperature.

Bisfuran-s-tetrazine (FTz) and its copolymers with cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) and benzo[1,2-b:4,5-b']dithiophene (BDT) (PCPDTFTz and PBDTFTz) are prepared with the alternating s-tetrazine and CPDT or BDT units bridged by a furan ring. Their optical and electrochemical properties are studied and compared with their thiophene analogs (PCPDTTTZ-out and PCPDTTTz-in), in which the bridging unit is 4-hexylthiophene or 3-hexylthiophene, respectively. Bulk heterojunction (BHJ) solar cells fabricated from these polymers with PC(sub)71BM have a power conversion efficiency (PCE) of 0.8 percent, which is much lower than that from the PCPDTTTz-out analog (3.2 percent), due to the low steric hindrance of the furan polymers in the absence of alkyl substitution on the furan ring.

We demonstrated, for the first time, that 3,6-bis(3-hexylthien-2-yl)-s-tetrazine (TTz) with hexyl group at the 3-position of thiophene rings can be prepared using a modified sulfur-assisted Pinner synthesis. Although the hexyl group creates large steric hindrance to the tetrazine ring formation reaction, and the reaction under a traditional condition only produces trace amount of the target product, the yield of this reaction under a modified reaction condition using anhydrous hydrazine at 68 °C can reach 65%. Two new copolymers of the resulting TTz and hexyl- or 2-ethylhexyl-substituted cyclepentadithiophene have been prepared. The polymers show a broader light absorption in film than in solution attributing to the large distribution of effective conjugation length of polymer chain due to the existence of both cis- and trans-orientations of the 3-hexylthiophene units in the planar polymer chain in solid state. Although the polymers show a narrow band gap and a deep HOMO level, which are desirable for generating an efficient light absorption and a larger open circuit voltage (V oc ) of the resulting solar cell devices, the device performance is not as good as expected. It is attributed to the random distribution of the cis- and trans-conformations along the polymer chain.

In this paper, we have comparatively investigated the stability of superhydrophobic behaviors of fresh and biomimetic lotus leaf surfaces under controlled water condensation conditions. The binary micro/nano structures of the superhydrophobic surfaces are observed with electron micrographs. Contact and sliding angles are evaluated by syringing water droplets on the substrates with surface temperatures and humidity precisely controlled between -10 and 30 °C, and RH = 10, 30, 60, and 90%. According to the calculations on the solid-liquid contact area fraction in different environmental conditions based on a micro/nano binary structure model, the effects of condensed water on superhydrophobic surfaces are assessed quantitatively. Both the calculated and experimental results indicate that the temperature difference between surface temperature and the dew point during measurement is essential to the occurrence of water condensation while the effect of condensation on the surface wettability also depends on the topology of hierarchical structured surfaces. The loss of water repellency that usually appears on the artificial superhydrophobic surface under low temperature and high humidity conditions is proved to be reversible, showing a bidirectional transition of the equilibrium state between Wenzel and Cassie-Baxter. © 2011 American Chemical Society.

The photophysical properties of a series of 9,9′-dioctylfluorene copolymers containing 1,3,4-oxadiazole units (PF1Ox, PF2Ox, PF3Ox, and PF4Ox) as well as a copolymer containing 9,9-dioctylfluorene, 1,3,4-oxadiazole, and N-octylcarbazole (PFOxCz) have been characterized by fluorescence and time-resolved absorption spectroscopy. It was observed that the photophysical data of PF2Ox, PF3Ox, and PF4Ox were almost coincident (λem = 426 nm, ϕfl = 0.38) and somewhat different from those of PF1Ox (λem = 404 nm, ϕfl = 0.34) and PFOxCz (λem = 472 nm, ϕfl = 0.39). These differences are attributed to the influence of the largest Ox percentage in the polymer (PF1Ox) or to the presence of a strong electron-donor carbazole unit (PFOxCz). In transient absorption spectroscopy the presence of triplet excitons (λ = 350 and 740 nm, quenched by oxygen), positive polarons (λ = 400 and 530 nm, quenched by triethylamine), and photoeject electrons (absorption onset 800 nm, quenched by oxygen) was observed for PFnOx (n = 1, 2, 3, 4...

A comb copolymer with a fluorinated FPAE main chain and narrowly dispersed PMS graft chains has been prepared. The micellization behavior of this copolymer in a methanol/acetone mixture was studied. DLS studies showed hydrodynamic diameters of the micelles between 50 and 80 nm, while the diameters of dry micelles were ≈40 nm in TEM images. Micelle films with an interesting porous composite structure of nanofibers bearing micelle particles on the surface have been prepared by double coating the micelle solution. Superhydrophobicity with a WCA of 165° and a sliding angle of 3° was observed. As comb copolymers can adjust their molecular weight and block length independently, materials with a high physical strength and controllable morphological structure can be obtained.

While stable polymer electrochromic properties are mainly realized from the electrochemical oxidation of p-type conjugated polymers, in this paper we report that stable electrochromic properties can also be easily achieved by electrochemical reduction of n-type polymers, such as PF4Ox, an alternating copolymer of quater(9,9-dioctylfluorene) and oxadiazole. The introduction of the strong electron-accepting oxadiazole unit into the poly(9,9-dioctylfluorene) main chain promoted the stability of the polymer in the electrochemical reduction. The copolymer film displayed an excellent elecrochromic property upon electrochemical reduction, which turned the colorless film at the neutral state to rosy-red at the electron charged state with a switching time of 1.1 s. The film exhibited a high stability during the electrochromic test, having only 30% loss of the transmittance change in 500 potential square-wave cycles. Fourier transform infrared (FT-IR) study revealed that decay of the electrochromic performance of the film was associated with the formation of fluorenone and quinone defects on the fluorene unit in the copolymer chain. The laser flash photolysis test showed the monomer unit had a high potential to localize an electron and became highly vulnerable to be attacked by oxygen to form the defects. These defects would act as charge carrier traps and produced a pair of inner peaks at -1.84 and 1.03 V in the cyclic voltammetry test of the copolymer film.

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) enriched by a conjugated polymer extraction process have been actively studied for various applications in both electronics and optoelectronics. Although the resulting tube samples usually have high sc-purity and concentration, SWCNT networks from such dispersions typically contain residual conjugated polymer that may degrade device performance and its removal remains a challenge while maintaining uniform, dense SWCNT thin film networks. In this study, a novel polymer–SWCNT combination based on an alternating bisfuran-s-tetrazine and benzo[1,2-b:4,5-b′]dithiophene copolymer abbreviated as PBDTFTz is proposed. This polymer decomposes at >250 °C or under UV irradiation. In situ transistor characterization under laser irradiation confirms the polymer decomposition. The study of the tube network in the transistor channel at various channel lengths reveals significantly reduced contact resistance attributed to removal of the wrapping PBDTFTz polymer. In ammonia sensing experiments, sc-SWCNT networks demonstrate rapid and reversible responses, while the unwrapped nanotube networks prove superior in terms of signal to noise ratio and a detection limit of 2.5 ppb is calculated, almost four times better than polymer wrapped nanotubes.

A set of fluorene copolymers designed to introduce electron donor/acceptor structures in the polymer chain that could eventually produce more efficient charge separation with long lifetimes has been prepared. To validate our approach, herein we report photoluminescence and laser flash photolysis measurements of the series of alternating specially functionalized fluorene copolymers. The copolymers contain 9,9-dioctylfluorene and N-octylcarbazole, oxadiazole, and oxadiazole-octafluorobiphenyl-oxadiazole units. It appears that the copolymer with the longest charge separated state lifetime and the highest charge separation quantum yield of the series is an alternating copolymer of a N-octylcarbazole and trifluorene units in which two fluorenes were attached with hydroxyhexyl side groups and the central fluorene with octyl side group at C-9 positions, respectively. These photophysical data suggest that this polymer a good candidate for photovoltaic cell and polymer light-emitting diode applications.