Cellulose‐Based Ionogels for Paper Electronics

A new class of biofriendly ionogels produced by gelation of microcellulose thin films with tailored 1‐ethyl‐3‐methylimidazolium methylphosphonate ionic liquids are demonstrated. The cellulose ionogels show promising properties for application in flexible electronics, such as transparency, flexibility, transferability, and high specific capacitances of 5 to 15 μF cm^?2. They can be laminated onto any substrate such as multilayer‐coated paper and act as high capacitance dielectrics for inorganic (spray‐coated ZnO and colloidal ZnO nanorods) and organic (poly[3‐hexylthiophene], P3HT) electrolyte‐gated field‐effect transistors (FETs), that operate at very low voltages (<2 V). Field‐effect mobilities in ionogel‐gated spray‐coated ZnO FETs reach 75 cm² V^?1 s^?1 and a typical increase of mobility with decreasing specific capacitance of the ionogel is observed. Solution‐processed, colloidal ZnO nanorods and laminated cellulose ionogels enable the fabrication of the first electrolyte‐gated, flexible circuits on paper, which operate at bending radii down to 1.1 mm.     

Quantification of four major metabolites of embryotoxic N-methyl- and N-ethyl-2-pyrrolidone in human urine by cooled-injection gas chromatography and isotope dilution mass spectrometry

N-Methyl- and N-ethyl-2-pyrollidone (NMP and NEP) are frequently used industrial solvents and were shown to be embryotoxic in animal experiments. We developed a sensitive, specific, and robust analytical method based on cooled-injection (CIS) gas chromatography and isotope dilution mass spectrometry to analyze 5-hydroxy-N-ethyl-2-pyrrolidone (5-HNEP) and 2-hydroxy-N-ethylsuccinimide (2-HESI), two newly identified presumed metabolites of NEP, and their corresponding methyl counterparts (5-HNMP, 2-HMSI) in human urine. The urine was spiked with deuterium-labeled analogues of these metabolites. The analytes were separated from urinary matrix by solid-phase extraction and silylated prior to quantification. Validation of this method was carried out by using both, spiked pooled urine samples and urine samples from 56 individuals of the general population with no known occupational exposure to NMP and NEP. Interday and intraday imprecision was better than 8% for all metabolites, while the limits of detection were between 5 and 20 μg/L depending on the analyte. The high sensitivity of the method enables us to quantify NMP and NEP metabolites at current environmental exposures by human biomonitoring.     

Effect of SiC‐Reinforcement and Equal‐Channel Angular Pressing on Microstructure and Mechanical Properties of AA2017

This article deals with powder metallurgical production and modification of properties of a composite material based on an age‐hardenable Al–Cu alloy. The main objective is to improve the mechanical properties by particle reinforcement and equal‐channel angular pressing (ECAP). Our approach makes use of four hardening mechanisms: precipitation hardening, particle reinforcement, strain‐hardening, and grain boundary hardening associated with an ultrafine‐grained microstructure produced by ECAP. The main processing steps are high‐energy ball milling, hot‐isostatic pressing, extrusion, heat treatment, and a single ECAP pass. Microstructures are analyzed by optical microscopy, scanning electron microscopy, and scanning transmission electron microscopy. The mechanical properties are characterized by hardness measurements and quasi‐static tensile testing. Our experimental results show that the proposed processing route results in a nearly homogeneous distribution of SiC particles in the matrix. The combination of particle reinforcement and ECAP leads to an improvement of ultimate tensile strength by almost 300 MPa compared to the unreinforced alloy. A subsequent heat treatment leads to a further increase in hardness and strength that can be related to changes in the defect structure. Our study provides detailed information on how processing steps, microstructures, and mechanical behavior are interrelated in this technologically relevant class of materials.     

Parametric MRI of Water Diffusion in Breast Cancer

Diffusion MRI studies revealed specific morphological and physiological properties of MCF7 tumors implanted in the mammary gland of immunodeficient mice. These tumors mimic the histological and pathophysiological properties of human breast cancer in patients. The experiments were conducted by (1) applying varying diffusion gradient strengths, G_d, from 0 to 20 G/cm and a short diffusion time (t_d = 16 ms) in order to minimize the effect of restriction and exchange of water between the intra- and extracellular compartments, and (2) applying a strong constant gradient and diffusion times up to 96 ms, revealing water restriction and exchange. The normalized signal intensity was plotted against the diffusion weighting factor b , taking into account interaction with the imaging gradients. The curves were analyzed by applying a bi-exponential decay function assuming two exchanging water compartments, with fast and slow diffusion coefficients. The amplitudes and decay constants of the two exponents, a fast and a slow one, were related to the fraction and apparent diffusion coefficients of the extra- and intracellular water, respectively, considering contributions of restriction and exchange. During tumor progression the distribution of the diffusion parameters for the same experimental protocol varied and became less homogeneous. This was predominantly due to variations in the cellularity and increased necrosis. Upon treatment of the tumors with a new anti-estrogenic drug, tamoxifen methiodide, the changes in the diffusion parameters indicated increased cell swelling. Hence, this cytostatic response to treatment was detected before actual cell death was apparent. The potential capacity of diffusion MRI is of high clinical relevance and may help improve the noninvasive diagnosis and followup of treatment of this devastating disease.     

Size dependence of the adsorption energy of CO on metal nanoparticles: a DFT search for the minimum value

With a density functional theory method, we studied computationally the size dependence of adsorption properties of metal nanoparticles for CO as a probe on Pd(n) clusters with n = 13-116 atoms. For large particles, the values slowly decrease with cluster size from the asymptotic value for an (ideal) infinite surface. For clusters of 13-25 atoms, starting well above the asymptotic value, the adsorption energies drop quite steeply with increasing cluster size. These opposite trends meet in an intermediate size range, for clusters of 30-50 atoms, yielding the lowest adsorption energies. These computational results help to resolve a controversy on the size-dependent behavior of adsorption energies of metal nanoparticles.     

Measurement and Prediction of the Thermal Conductivity of Tricyanomethanide- and Tetracyanoborate-Based Imidazolium Ionic Liquids

The thermal conductivity of ten ionic liquids (ILs) based on the anions \([\mathrm{C(CN)}_{3}]^{-}\) (tricyanomethanide) and \([\mathrm{B(CN)}_{4}]^{-}\) (tetracyanoborate) carrying a homologous series of the [alkyl-MIM] \(^{+}\) (1-alkyl-3-methylimidazolium) cations [EMIM] \(^{+}\) (ethyl), [BMIM] \(^{+}\) (butyl) [HMIM] \(^{+}\) (hexyl), [OMIM] \(^{+}\) (octyl), [DMIM] \(^{+}\) (decyl) was measured by a steady-state guarded parallel-plate instrument in the temperature range between (283.15 and 353.15) K at atmospheric pressure with a total uncertainty of 5 % ( \(k\,=\,2\) ). Furthermore, the refractive index required for data evaluation and the density, which is an important property in the developed prediction method for the thermal conductivity, were determined. In general, the measured thermal conductivities of the probed ILs decrease with increasing temperature and increasing alkyl-chain length of the cation. Regarding the influence of the anion, somewhat smaller values for the \([\mathrm{B(CN)}_{4}]^{-}\) -based ILs compared to the \([\mathrm{C(CN)}_{3}]^{-}\) -based ILs carrying the same cation are observed. Our previously developed simple prediction method for the thermal conductivity of ILs at 293.15 K using only information on the molar mass and the density could be improved. By the combination of this approach with the temperature dependence of the density, an extended empirical correlation additionally describing the temperature dependence of the thermal conductivity of ILs is recommended. This correlation represents all experimental thermal-conductivity data in the literature with a standard deviation of less than 7 %.     

Formation and catalytic activity of partially oxidized Pd nanoparticles

Combining multi molecular beam (MB) experiments and in-situ time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we have studied the formation and catalytic activity of Pd oxide species on a well-defined Fe₃O₄ supported Pd model catalyst. It was found that for oxidation temperatures up to 450 K oxygen predominantly chemisorbs on metallic Pd whereas at 500 K and above (~10⁻⁶ mbar effective oxygen pressure) large amounts of Pd oxide are formed. These Pd oxide species preferentially form a thin layer at the particle/support interface. Their formation and reduction is fully reversible. As a consequence, the Pd interface oxide layer acts as an oxygen reservoir providing oxygen for catalytic surface reactions. In addition to the Pd interface oxide, the formation of surface oxides was also observed for temperatures above 500 K. The extent of surface oxide formation critically depends on the oxidation temperature resulting in partially oxidized Pd particles between 500 and 600 K. It is shown that the catalytic activity of the model catalyst for CO oxidation decreases significantly with increasing surface oxide coverage independent of the composition of the reactants. We address this deactivation of the catalyst to the weak CO adsorption on Pd surface oxides, leading to a very low reaction probability.     

An improved single crystal adsorption calorimeter for determining gas adsorption and reaction energies on complex model catalysts

A new ultrahigh vacuum microcalorimeter for measuring heats of adsorption and adsorption-induced surface reactions on complex single crystal-based model surfaces is described. It has been specifically designed to study the interaction of gaseous molecules with well-defined model catalysts consisting of metal nanoparticles supported on single crystal surfaces or epitaxial thin oxide films grown on single crystals. The detection principle is based on the previously described measurement of the temperature rise upon adsorption of gaseous molecules by use of a pyroelectric polymer ribbon, which is brought into mechanical∕thermal contact with the back side of the thin single crystal. The instrument includes (i) a preparation chamber providing the required equipment to prepare supported model catalysts involving well-defined nanoparticles on clean single crystal surfaces and to characterize them using surface analysis techniques and in situ reflectivity measurements and (ii) the adsorption∕reaction chamber containing a molecular beam, a pyroelectric heat detector, and calibration tools for determining the absolute reactant fluxes and adsorption heats. The molecular beam is produced by a differentially pumped source based on a multichannel array capable of providing variable fluxes of both high and low vapor pressure gaseous molecules in the range of 0.005-1.5 × 10(15) molecules?cm(-2)?s(-1) and is modulated by means of the computer-controlled chopper with the shortest pulse length of 150 ms. The calorimetric measurements of adsorption and reaction heats can be performed in a broad temperature range from 100 to 300 K. A novel vibrational isolation method for the pyroelectric detector is introduced for the reduction of acoustic noise. The detector shows a pulse-to-pulse standard deviation ≤15 nJ when heat pulses in the range of 190-3600 nJ are applied to the sample surface with a chopped laser. Particularly for CO adsorption on Pt(111), the energy input of 15 nJ (or 120 nJ?cm(-2)) corresponds to the detection limit for adsorption of less than 1.5 × 10(12) CO molecules?cm(-2) or less than 0.1% of the monolayer coverage (with respect to the 1.5 × 10(15) surface Pt atoms?cm(-2)). The absolute accuracy in energy is within ～7%-9%. As a test of the new calorimeter, the adsorption heats of CO on Pt(111) at different temperatures were measured and compared to previously obtained calorimetric data at 300 K.