The thermal stability of poly(3-hexylthiophene) (P3HT) in its molten state was investigated in air and nitrogen atmospheres under no illumination conditions, with the aim of testing the feasibility of processing it using polymer melt techniques. A large set of different experimental characterization techniques was used including thermogravimetric analysis (TGA), rotational rheometry, infrared spectroscopy (FTIR-ATR), proton nuclear magnetic resonance spectroscopy (1H-NMR), gel permeation chromatography (GPC), UV-Vis and fluorescence spectroscopy. The results obtained strongly suggest that the processing of P3HT in its molten state is possible, without noticeable degradation, if carried out under nitrogen atmosphere and if the processing (residence) times are relatively short. Conversely, as expected, in a normal air atmosphere P3HT degrades rapidly at temperatures above its melting point. The effect of PCBM on the thermal stability of P3HT:PCBM blends in the molten state was also studied using TGA, and in air atmosphere PCBM is shown to delay oxidation. 相似文献
The development of safe and long‐lasting all‐solid‐state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic‐scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long‐range as well as short‐range Li ion dynamics in the glass‐ceramic Li7P3S11. Li+ diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li+ diffusivity, which is reflected in a so‐called diffusion‐induced 6Li NMR spin‐lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×108 s?1, which corresponds to a Li+ ion conductivity in the order of 10?4 to 10?3 S cm?1. Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li7P3S11. In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through‐going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li7P3S11 crystallites. As a result of this, long‐range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long‐range ionic conduction. If we are to succeed in solid‐state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation of samples that are free of any amorphous regions that block fast ion transport. 相似文献
Solid bases, such as SBA‐15‐oxynitrides, have attracted considerable interest for potential applications as catalysts in important industrial processes. Reported herein is that by simply tuning the temperature of nitridation (ammonolysis), the catalytic activity of these solid bases can be enhanced. Solid‐state NMR spectroscopy and XPS studies provided the reasoning behind this change in activity. 相似文献
The dynamics of poly(dimethylsiloxane) in its inclusion compound with γ‐cyclodextrin are elucidated using modern fast‐MAS solid‐state NMR techniques. Measurements of methyl 1H–1H and 1H–13C dipolar coupling constants indicate that the polymer undergoes a uniform motion, rendering all methyl groups equivalent. The dynamics of the Si—C bond is characterized by either a dynamic order parameter of S = 0.72, or, assuming a stably rotating helical structure, an inclination angle of 73° relative to the rotation axis. 相似文献
It is very important to monitor the characteristics of triacylglycerol crystal network in fats, as these crystals have an impact on many food properties such as texture, sensory taste, and extended shelf life. Although time-domain NMR (TD-NMR) is now the reference technique to determine the solid fat index in food, the entire possibilities of this technique are not used. Some NMR studies have been performed to determine its power for the discrimination of polymorphism. In this study, extended investigations proved that TD-NMR could evaluate triacylglycerol (TA) polymorphism, independently from temperature and chain length. Study of the dipolar interactions through second moment M(2), which is characteristic of proton mobility in solid-state samples, provided a new understanding of the structural organization of crystal molecules. Proton spin-lattice relaxation, which has been proved to be a true probe of polymorphism, has provided information on crystal networks. Combination of the two techniques revealed two very interesting kinds of results, i.e. the presence of a minimum spin-lattice relaxation time T(1) for tristearin alpha, which is a characteristic of a dynamic molecular process, and differences in behavior between long and short chain lengths, both at a molecular and a crystal level. 相似文献
By changing the surfactant/water ratio , nanoparticles of the iron(II) spin crossover material, [Fe(NH2‐trz)3]Br2 ? 3 H2O (with NH2‐trz=4‐amino‐1,2,4‐triazole), have been synthesised from 1 μm down to 30 nm (see figure). Magnetic and reflectivity experiments indicate that the critical size for observing a thermal hysteresis in this 1D polymer family is around 50 nm, and powder X‐ray diffraction shows that particles of about 30 nm are constituted by about one coherent domain.
The surface hydroxyl groups of γ‐alumina dehydroxylated at 500 °C were studied by a combination of one‐ and two‐dimensional homo‐ and heteronuclear 1H and 27Al NMR spectroscopy at high magnetic field. In particular, by harnessing 1H–27Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the 1H magic‐angle spinning (MAS) NMR spectrum was demonstrated thanks to 1H–27Al RESPDOR (resonance‐echo saturation‐pulse double‐resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {1H}‐27Al dipolar heteronuclear multiple quantum correlation (D‐HMQC), which was used to establish a first coordination map. Then, in combination with 1H–1H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO2 reactivity with alumina. 相似文献