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Time-of-flight Technique (time-of-flight + technique)
Selected AbstractsThe Impact of Polymer Regioregularity on Charge Transport and Efficiency of P3HT:PCBM Photovoltaic DevicesADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Ralf Mauer Abstract The charge transport in pristine poly(3-hexylthiophene) (P3HT) films and in photovoltaic blends of P3HT with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) is investigated to study the influence of charge-carrier transport on photovoltaic efficiency. The field- and temperature dependence of the charge-carrier mobility in P3HT of three different regioregularities, namely, regiorandom, regioregular with medium regioregularity, and regioregular with very high regioregularity are investigated by the time-of-flight technique. While medium and very high regioregularity polymers show the typical absorption features of ordered lamellar structures of P3HT in the solid state even without previous annealing, films of regiorandom P3HT are very disordered as indicated by their broad and featureless absorption. This structural difference in the solid state coincides with partially non-dispersive transport and hole mobilities µh of around 10,4 and 10,5,cm2 V,1 s,1 for the high and medium regioregularity P3HT, respectively, and a slow and dispersive charge transport for the regiorandom P3HT. Upon blending the regioregular polymers with PCBM, the hole mobilities are typically reduced by one order of magnitude, but they do not significantly change upon additional post-spincasting annealing. Only in the case of P3HT with high regioregularity are the electron mobilities similar to the hole mobilities and the charge transport is, thus, balanced. Nonetheless, devices prepared from both materials exhibit similar power conversion efficiencies of 2.5%, indicating that very high regioregularity may not substantially improve order and charge-carrier transport in P3HT:PCBM and does not lead to significant improvements in the power-conversion efficiency of photovoltaic devices. [source] Mapping of unstressed lattice parameters using pulsed neutron transmission diffractionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2002Javier Roberto Santisteban Stress measurement by neutron diffraction depends critically on knowledge of the unstressed lattice parameter (a0) of the specimen under study. As a result, measurement of stress profiles in components where a0 is not homogeneous throughout the sample, such as welds or carburized surfaces, can be particularly difficult. An efficient solution to this problem is proposed based on the pulsed neutron transmission diffraction technique. This technique exploits the sharp steps in intensity, the so-called Bragg edges, appearing in the transmitted neutron spectra of polycrystalline materials, such steps being produced by coherent scattering from lattice planes. The position of these Bragg edges as defined by the time-of-flight technique is used to determine precisely local interplanar distances. In this work it is shown that the unstressed lattice parameter of thin specimens subjected to plane stress fields can be defined by recording transmission spectra at different sample inclinations, in complete analogy with the sin2, technique used in X-ray diffraction. Moreover, by using an array of detectors it is possible to produce a radiographic `image' of a0 for plane specimens or thin sections out of three-dimensional ones. The capability of the technique is exemplified by mapping the changes in a0 for a ferritic weld that was used as a round robin sample in an international program for standardization of stress measurements by neutron diffraction. [source] Physical characteristics and aerosolization performance of insulin dry powders for inhalation prepared by a spray drying methodJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 7 2007Yu You The objective of this study was to investigate the influence of formulation excipients on the physical characteristics and aerosolization performance of insulin dry powders for inhalation. Insulin dry powders were prepared by a spray drying technique using excipients such as sugars (trehalose, lactose and dextran), mannitol and amino acids (L-leucine, glycine and threonine). High performance liquid chromatography and the mouse blood glucose method were used for determination of the insulin content. The powder properties were determined and compared by scanning electron microscopy, thermo-gravimetric analysis and size distribution analysis by a time-of-flight technique. The in-vitro aerosolization behaviour of the powders was assessed with an Aerolizer inhaler using a twin-stage impinger. Powder yield and moisture absorption were also determined. Results showed that there was no noticeable change in insulin content in any of the formulations by both assay methods. All powders were highly wrinkled, with median aerodynamic diameters of 2,4 ,m, and consequently suitable for pulmonary administration. The tapped density was reduced dramatically when glycine was added. The powders containing mannitol, with or without L-Ieucine, were less sensitive to moisture. The highest respirable fraction of 67.3 ± 1.3% was obtained with the formulation containing L-leucine, in contrast to formulations containing glycine and threonine, which had a respirable fraction of 11.2 ± 3.9% and 23.5 ± 2.5%, respectively. In addition, powders with good physical properties were achieved by the combination of insulin and trehalose. This study suggests that L-leucine could be used to enhance the aerosolization behaviour of the insulin dry powders for inhalation, and trehalose could potentially be used as an excipient in the formulations. [source] Synthesis and polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene with Ziegler,Natta, rhodium, and palladium complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2005J. Gonzalo Rodríguez Abstract The synthesis and polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene was carried out with a homogeneous vanadium acetylacetonate/aluminum triethyl catalyst system, a bis(rhodium chloride cycloocta-1,5-diene) complex, and a palladium/trimethylsilyl complex. In all cases, the main fraction was a polymer with a stereoregular structure. The polymerization with the vanadium catalyst gave a polymer fraction in a low yield. The polymerization of (E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene with the soluble rhodium complex gave a polymer in a high yield. The soluble palladium/chlorotrimethylsilane complex gave a polymer in a good yield. On the basis of the spectroscopic data, the poly{(E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene)} obtained, in all cases, showed a cis,transoidal stereoregular structure. The molecular mass of poly{(E)- p -[(p -methoxyphenyl)-2-ethenyl]phenylacetylene)} was determined by the matrix-assisted laser desorption/ionization time-of-flight technique. The kinetics of the reaction were analyzed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6438,6444, 2005 [source] | ||||||||||