Mixed Charge Research Articles

Highly Efficient Solid‐State Near‐Infrared Emitting Material Based on Triphenylamine and Diphenylfumaronitrile with an EQE of 2.58% in Nondoped Organic Light‐Emitting Diode

The development of efficient near‐infrared (NIR) emitting material is of current focus. Donor–acceptor (D–A) architecture has been proved to be an effective strategy to obtain narrow energy gap. Herein, a D–A‐type NIR fluorescent compound 2,3‐bis(4′‐(diphenylamino)‐[1,1′‐biphenyl]‐4‐yl)fumaronitrile (TPATCN) is synthesized and fully characterized. As revealed by theoretical calculations and photophysical experiments, TPATCN exerts the advantages of the relatively large dipole moment of the charge transfer state and a certain degree of orbital overlap of the local excited state. A highly mixed or hybrid local and charge transfer excited state might occur to simultaneously achieve both a large fraction of singlet formation and a high quantum efficiency in D–A system. TPATCN exhibits strong NIR fluorescence with the corresponding thin film quantum efficiency of 33% and the crystal efficiency of 72%. Remarkably, the external quantum efficiency of nondoped NIR organic light‐emitting diode (OLED) reaches 2.58% and remains fairly constant over a range of 100–300 mA cm−2, which is among the best results for NIR OLEDs reported so far.

Double pion photoproduction off Ca-40

The pbotoproduction of pi(0)pi(0) and pi(0)pi(+/-) pairs off Ca-40 has been investigated with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data have been taken for incident photon energies in the energy range from 200-820MeV. Total cross-sections have been extracted from threshold up to the maximum photon energy and invariant-mass distributions of the pion pairs have been obtained for incident photon energies between 400-500 MeV and 500 550 MeV. The double pi(0) invari ant- mass distributions show some relative enhancement with respect to the mixed charge channel at small invariant masses. The effects are smaller than previously observed for lead nuclei and the distributions do not significantly deviate from carbon data. The data are in good agreement with the results of recent calculations in the framework of the BUU model, with careful treatment of final-state interaction effects but without an explicit in-medium modification of scalar, iso-scalar pion pairs. This means that for Ca most of the experimentally observed effect can be explained by final-state interactions. Only at low incident photon energies there is still a small low mass enhancement of the double pi(0) data over the BUU results.

Precise colloids with tunable interactions for confocal microscopy.

Model colloidal systems studied with confocal microscopy have led to numerous insights into the physics of condensed matter. Though confocal microscopy is an extremely powerful tool, it requires a careful choice and preparation of the colloid. Uncontrolled or unknown variations in the size, density, and composition of the individual particles and interactions between particles, often influenced by the synthetic route taken to form them, lead to difficulties in interpreting the behavior of the dispersion. Here we describe the straightforward synthesis of copolymer particles which can be refractive index- and density-matched simultaneously to a non-plasticizing mixture of high dielectric solvents. The interactions between particles are accurately tuned by surface grafting of polymer brushes using Atom Transfer Radical Polymerization (ATRP), from hard-sphere-like to long-ranged electrostatic repulsion or mixed charge attraction. We also modify the buoyant density of the particles by altering the copolymer ratio while maintaining their refractive index match to the suspending solution resulting in well controlled sedimentation. The tunability of the inter-particle interactions, the low volatility of the solvents, and the capacity to simultaneously match both the refractive index and density of the particles to the fluid opens up new possibilities for exploring the physics of colloidal systems.

Impact of poly(vinyl alcohol) adsorption on the surface characteristics of mixed oxide Mn x O y –SiO2

The poly(vinyl alcohol) (PVA) influence on the adsorption and electrokinetic properties of the mixed oxide Mn x O y –SiO2/polymer solution system was examined. Three oxides differing with the Mn x O y contents were applied (0.2; 1 and 3 mmol/g SiO2, respectively). The PVA with the molecular weight 100 kDa was characterized with the acetate groups content equal to 14 %. Adsorption, solid surface charge and zeta potential measurements were made as a function of solution pH (3–10). The obtained results showed that the PVA adsorption amount strongly depends on not only the solution pH, but also manganese oxide content on the mixed oxide surface. The higher solution pH value (or Mn x O y content) is, the higher polymer adsorption is obtained. The PVA addition to the solid suspension causes minimal changes of the mixed oxide surface charge density, whereas the zeta potential of solid particles increases significantly in the polymer presence.

Tuning the Emission of Cationic Iridium (III) Complexes Towards the Red Through Methoxy Substitution of the Cyclometalating Ligand.

The synthesis, characterization and evaluation in solid-state devices of a series of 8 cationic iridium complexes bearing different numbers of methoxy groups on the cyclometallating ligands are reported. The optoelectronic characterization showed a dramatic red shift in the absorption and the emission and a reduction of the electrochemical gap of the complexes when a methoxy group was introduced para to the Ir-C bond. The addition of a second or third methoxy group did not lead to a significant further red shift in these spectra. Emission maxima over the series ranged from 595 to 730 nm. All complexes possessing a motif with a methoxy group at the 3-position of the cyclometalating ligands showed very short emission lifetimes and poor photoluminescence quantum yields whereas complexes having a methoxy group at the 4-position were slightly blue shifted compared to the unsubstituted parent complexes, resulting from the inductively electron withdrawing nature of this directing group on the Ir-C bond. Light-emitting electrochemical cells were fabricated and evaluated. These deep red emitters generally showed poor performance with electroluminescence mirroring photoluminescence. DFT calculations accurately modelled the observed photophysical and electrochemical behavior of the complexes and point to an emission from a mixed charge transfer state.

Thermal analysis of large-capacity LiFePO4 power batteries for electric vehicles

Excellent design of a thermal management system requires good understanding of the thermal behaviors of power batteries. In this study, the electrochemical and heat performances of a prismatic 40 Ah C/LiFePO4 battery are investigated with a focus on the influence of temperature on cell capacity in a mixed charge–discharge cycle. In addition, the heat generation and energy efficiency of a battery are determined during charge and discharge at different current rates. The experimental results indicate that in certain temperature ranges, both the charging and discharging capacities increase significantly as the temperature increases. In addition, the energy efficiency reaches more than 95% when the battery runs at a current rate of 0.33 C–2 C and temperature of 25–45 °C. A thermal mathematical model based on experimentally obtained internal resistances and entropy coefficients is developed. Using this model, the increase in the battery temperature is simulated based on specific heat values that are measured experimentally and calculated theoretically. The results from the simulation indicate that the temperature increase agrees well with the experimental values, the measured specific heat provides better results than the calculated specific heat and the heat generated decreases as the temperature increases.

Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O 3/HfO 2 tunnel oxide.

In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-015-0957-5) contains supplementary material, which is available to authorized users.

Synthesis, Characterization, and Properties of Doubly Alkynyl Bridging Dinuclear Cyclometalated Iridium(III) Complexes

Bis(cyclometalated) diiridium complexes [Ir(ppy)2(μ–κCα:η2-C≡CR)]2 (R = Tol 1, C6H4OMe-4 2, 1-Np 3, SiMe3 4, tBu 5), stabilized by a double alkynyl bridging system, have been synthesized by alkynylation of [Ir(ppy)2(μ-Cl)]2 with excess of the appropriate LiC≡CR (1:6 or 1:10 molar ratio). Complexes 1–3 were alternatively generated by treatment of [Ir(ppy)2(MeCN)2](OTf) with 2.5 equiv of LiC≡CR. However, the related reaction with LiC≡CtBu evolves with the formation of mixtures from which the unexpected dinuclear complex [Ir(ppy)2(μ-CH2CN)]2 6 was crystallized, as confirmed by X-ray diffraction studies. Complexes 1–5 have been characterized by NMR, IR, absorption and emission spectroscopies, cyclic voltammetry, and mass spectrometric methods. Characterization indicates that 1–3 and 5 are obtained as a unique diastereoisomer (ΛΛ/ΔΔ), whereas 4 gives the two diastereoisomers (ΔΛ and ΛΛ/ΔΔ). Single crystals of [Ir(ppy)2(μ-C≡CTol)]2 1 contains the inversion related ΛΛ/ΔΔ isomers, and crystals of 4 (chosen from a mixture of two different types of crystals) consist of the meso-ΔΛ isomer. Electrochemical studies showed the presence in 1–3 and 5 of two consecutive one-electron-oxidation IrIII/IrIV processes, whereas 4 displayed only one irreversible oxidation peak. In degassed fluid solutions, complexes 1–5 are emissive in the 505–515 nm region with quantum yields higher (ϕ = 0.007–0.024) than that of the dichloro bridged precursor (0.0037). The influence of the alkynyl substituent in the emissive state at room and at low temperatures has been investigated. For the naphthylacetylide derivative 3, a clear switch from a mixed charge transfer 3MLCT/3L′LCT excited state at 298 K (515 nm) to a characteristic long-lived low lying naphthalene emission at low temperature (77 K) is observed. DFT and TD-DFT calculations were performed on complexes 1 and 3 in the ground and triplet states to gain insight into the structural, electronic, and photophysical properties.

Discovery of protein- and DNA-imperceptible nanoparticle hard coating using gel-based reaction tuning.

The seemingly inevitable protein corona appears to be an insurmountable obstacle to wider application of functional nanomaterials in biotechnology. The accumulation of serum proteins can block targeting functionalities and alter the in vivo fate of these nanomaterials. Here we demonstrate a method to generate non-stick, robustly passivated functional nanoparticles (NPs) using a tailored silica coating. We apply agarose gel electrophoresis to sensitively evaluate protein binding to NPs with different surface chemistry. Using gel banding and retardation as a read-out for protein adsorption, we optimize the surface chemistry to yield a mixed charge surface which displays remarkable binding resistance to a wide range of serum proteins and nucleic acids. The hard silica shell also protects the functional NP core in harsh environments (down to pH 1) while still showing the ability to be targeted for cellular uptake with little or no non-specific binding.

Usefulness of Quartzites for the Production of Ferrosilicon

The selection of quartzites most suitable for the production of ferrosilicon is realized by way of time-consuming industrial trials or laboratorial studies of, among others, the ability of the silica contained in quartzite to form silicon carbide with a selected reducer. Under industrial conditions, the basic criterion for the evaluation of the suitability of a raw material for the production of ferrosilicon are the technical and economic indicators of the process. Under laboratorial conditions, simple and reliable research methods are searched for, which would allow to determine the usefulness of quartzite in the process of carbon silica reduction. The article discusses comparative thermogravimetric studies as well as alternative investigations of the specific heat of three selected quartzites which fulfill the chemical composition criterion, used in the mixed charge as raw materials for ferrosilicon FeSi75 smelting.

Correction: Spin mixed charge transfer states of iridium complex Ir(ppy)3: transient absorption and time-resolved photoluminescence

Correction for ‘Spin mixed charge transfer states of iridium complex Ir(ppy)3: transient absorption and time-resolved photoluminescence’ by Mohan Singh Mehata et al., RSC Adv., 2015, 5, 34094–34099.

Spin mixed charge transfer states of iridium complex Ir(ppy)3: transient absorption and time-resolved photoluminescence

Transient absorption and time-resolved PL together with quantum chemistry calculations demonstrated the existence of multiple low-lying metal-to-ligand charge transfer states of Ir(ppy)3.

Corrosion of a Carbon Steel Cylindrical Band Exposed to a Concentrated NaCl Solution Flowing through an Annular Flow Cell

The corrosion kinetics of a carbon steel cylindrical band concentrically positioned in an annular flow cell exposed to a flow of concentrated unbuffered NaCl solution was investigated using linear sweep voltammetry and scanning electron microscopy techniques. These experiments employed a set of conditions of high NaCl concentration and low Reynolds number values. Assuming that the corrosion reaction is entirely under conditions of mixed charge transfer plus diffusion control mechanism on a bare metal surface, the corrosion process and local surface pH were simulated by applying mixed potential theory and a mass and charge balance on the metal surface, respectively. Changes in the corrosion rates, electrochemical parameter values for partial corrosion reactions, surface pH, and morphological attributes are discussed.

Experiment and simulation of a LiFePO4 battery pack with a passive thermal management system using composite phase change material and graphite sheets

A passive thermal management system (TMS) for LiFePO4 battery modules using phase change material (PCM) as the heat dissipation source to control battery temperature rise is developed. Expanded graphite matrix and graphite sheets are applied to compensate low thermal conductivity of PCM and improve temperature uniformity of the batteries. Constant current discharge and mixed charge–discharge duties were applied on battery modules with and without PCM on a battery thermal characteristics test platform. Experimental results show that PCM cooling significantly reduces the battery temperature rise during short-time intense use. It is also found that temperature uniformity across the module deteriorates with the increasing of both discharge time and current rates. The maximum temperature differences at the end of 1C and 2C-rate discharges are both less than 5 °C, indicating a good performance in battery thermal uniformity of the passive TMS. Experiments on warm-keeping performance show that the passive TMS can effectively keep the battery within its optimum operating temperature for a long time during cold weather uses. A three dimensional numerical model of the battery pack with the passive TMS was conducted using ANSYS Fluent. Temperature profiles with respect to discharging time reveal that simulation shows good agreement with experiment at 1C-discharge rate.

Efficient Charge Balance of Green Organic Light Emitting Diodes Using Mixed Charge Transporting Materials as the Host

The mixed layer for an emitting layer (EML) consists of two materials 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) without host material. A series of EML structures were fabricated with three types of single mixed layers (mixing ratio 2:1, 1:2) and double mixed layers (mixing ratio 2:1/1:2), and the EML of using double mixed layer was optimized. The maximum luminous efficiency (LE) and quantum efficiency (QE) were 62.07 cd/A, 18.92%, respectively. Moreover, the roll-off ratio of LE was 20.42% at 20,000 cd/m2. Interestingly, this result shows the roll-off ratio was reduced roughly 50% compared to the reference device.

Synthesis, structural characterization and spectroscopic properties of cobalt complexes with the 2,6-bis(8′-quinolinyl)pyridine ligand

Coordination of the 2,6-bis(8′-quinolinyl)pyridine (bqp) ligand to a cobalt (Co) core and its influence to electron spin and configuration on the structures and properties of the resulting complexes has been investigated. The homoleptic complexes Co(mer-bqp-κ3N,N′,N″)]2+ (1) and [Co(mer-bqp-κ3N,N′,N″)]3+ (2) were prepared and characterized. X-ray structure determinations of complexes 1 and 2 revealed twisted, near-octahedral arrangements relative to the cobalt center. The magnetic data for 1 is typical of those for distorted octahedral (i.e., D4h symmetry) high-spin d7 species despite the near-ideal octahedral coordination of the bqp ligand around the Co(II) core. Electronic spectra for 1 and 2 have been investigated and assigned. Both complexes exhibit intense π–π∗bqp ligand centered transitions in the UV region and low intensity mixed charge transfer transitions in the visible region. Neither complex strongly absorbs in visible spectral region. The electrochemistry of these compounds has been studied and compared to that of similar cobalt terpyridine compounds. A metal-centered Co2+/3+ redox wave and ligand-based reduction processes were observed for 1 and 2 in acetonitrile. The metal-centered redox potentials were reversible with potentials more positive than comparable cobalt-terpyridine complexes. Density functional theory (DFT) calculations of the electronic and ground state properties are in good agreement with the experimental data.

Small but powerful: co-assembly of polyether-based triblock terpolymers into sub-30 nm micelles and synergistic effects on cellular interactions.

We introduce a versatile ABC triblock terpoly- mer platform based on poly(ethylene oxide)-block-poly(allyl glycidyl ether)-block-poly(tert-butyl glycidyl ether) (PEO-b-PAGE-b-PtBGE) and subsequent functionalization of the PAGE segment with thiogalactose (hydroxyl), cysteamine (amino), and 2-mercaptopropionic acid (carboxy) by thiol-ene chemistry. These materials are used to prepare core-shell-corona micelles with a PtBGE core, a PAGE shell, and a PEO corona and sizes below 30 nm in aqueous media. We investigate the influence of different functional groups on micelle formation and cellular uptake. Moreover, co-assembly of differently functionalized materials allows to create micelles with a mixed shell and adjustable charge and, in that way, important characteristics such as cell uptake or cytotoxicity can be controlled. Furthermore, we demonstrate that even the uptake mechanism depends on the substitution pattern of the underlying triblock terpolymer.

Hemocompatibility of pseudozwitterionic polymer brushes with a systematic well-defined charge-bias control

In this study, a pseudozwitterionic surface bearing positively and negatively mixed charged moieties was developed as a potential hemocompatible material for biomedical applications. In this work, hemocompatility of pseudozwitterionic surface prepared from copolymerization of negatively charged 3-sulfopropyl methacrylate (SA) and positively charged [2-(methacryloyloxy)ethyl] trimethylammonium (TMA) was delineated. Mixed charge distribution in the prepared poly(TMA-co-SA)-grafted surface can be controlled by regulating TMA and SA monomer ratios via surface-initiated atom transfer radical polymerization. The effects of grafting composition and charge bias variations on blood compatibility of poly(TMA-co-SA)-grafted surface were reported. The protein adsorption on different poly(TMA-co-SA)-grafted surfaces from human plasma protein (fibrinogen, HSA, and γ-globulin) solutions was evaluated using an enzyme-linked immunosorbent assay. Blood platelet adhesion and time measurements on plasma clotting were conducted to determine the platelet activation on the grafted surface. It was found that the protein resistance and anti-blood cell adhesion of prepared surface can be precisely controlled by controlling the charge balance of TMA/SA compositions. In addition, different charge bias variations on the poly(TMA-co-SA)-grafted surface would induce electrostatic interactions between plasma proteins and prepared surfaces which lead to adsorptions of interfacial protein and blood cells, plasma clotting, and blood cell hemolysis. Results from this study suggest that the hemocompatility of mixed charged poly(TMA-co-SA)-grafted surface depends on the charge bias level. This provides a great potential for designing biomaterial with unique surface chemical structure which could be used in contact with human blood.

Sodium Alkyl Ether Sulfonates (SAES): Dual Anionic‐Nonionic Behavior in Synthetic Brine Having High Salinity and Hardness

AbstractDue to the presence of non‐sulfonated residual alkyl ether (AE), sodium alkyl ether sulfonate (SAES) may exhibit clear point‐cloud point solubilization behavior in brine. Accordingly, the effect of temperature on the compatibility of iC17EOxS (x = 7 and 10), nC17EO10S, along with their analogous nonionic surfactants iC17EOxH (x = 7 and 10) and nC17EO10, in addition to iC9EO14 in brine has been investigated. Depending on their molecular structures, these surfactants exhibited concentration‐dependent clear point and cloud point solubilization behavior. The cloud point was associated with the AE component whereas the clear point was attributed to the sulfonated one. Interestingly, an increase in the cloud point of the nonionic component with respect to the corresponding nonionic AE (100 % active) was observed. Adding iC9EO14 (100 % active) to iC17EO7S (xan = 0.0–0.362) resulted in a significant decrease in the clear point of iC17EO7S from above 100 °C to below 22 °C with a concomitant increase in iC17EO7/iC9EO14 mixture cloud point from 68 °C. (xan = 0) to 72 °C (xan = 0.325). This relatively modest increase by 4 °C was attributed to the interrelationship of different competitive mechanisms, namely an increase in mixed micelle charge with increasing xan, the dehydration of OE groups via ion (SO3−)‐dipole (O → CH2) interactions, and possible shielding of SO3− groups by iC9EO14 nearby extended EO groups. To the best of our knowledge, this is the first instance where dual anionic‐nonionic solubilization behavior of SAES in brine characterized by high salinity and hardness is being reported.

Efficient green phosphorescent tandem organic light emitting diodes with solution processable mixed hosts charge generating layer

A novel solution processable charge generating layer (CGL) that consists of 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN6)/Poly(N-vinylcarbazole) (PVK): 1,1-bis-(4-bis(4-tolyl)-aminophenyl) cyclohexene (TAPC) for a tandem green phosphorescent organic light emitting diode (PHOLED) is demonstrated. The use of orthogonal solvent to dissolve HATCN6 and PVK:TAPC is the key to overcome the interface erosion problem for the solution processed CGL. The current efficiency of the 2wt% TAPC mixed with PVK is the highest at 24.2cd/A, which is more than three-folds higher than that of the single device at 1000cd/m2.