ABSTRACT:A new approach for obtaining elastic polyimide-silica composites using a silanol sol prepared from water glass and the imide-containing elastic polymers (IEPs) with polytetramethyleneoxide (PTMO) soft-segment was investigated. Methods of increasing the degree of compatibility between the silica phase prepared from a silanol sol and IEPs obtained via elastic polyureas were examined. Elastic polyimide-silica composites were obtained by the thermal treatment at 200°C for 4 h in vacuo after N-methyl-2-pyrrolidone was evaporated from the IEP precursor solutions to which the silanol tetrahydrofuran solution and Bis(trimethoxysilylpropyl)amine (BisA) were added. The use of BisA possessing a reaction site with a carboxylic acid group on the IEP precursors improved the degree of compatibility between the IEPs and silica. Transparent composites were obtained when the concentration of SiO 2 was below 22 wt %. FT-IR analyses confirmed that the composite was a segmented hybrid material composed of the PTMO segment, the imide segment, and SiO 2 . The silica matrix obtained via silanol sol from water glass and the silica matrix obtained by the conventional sol-gel process with an alkoxysilane were essentially the same, and there was no significant loss of silicon due to incomplete hydrolysis of the alkoxides when preparing composites via the water glass route, in contrast to the situation that can occur in the case of the sol-gel route. Dynamic mechanical and thermal analyses suggested that microphase separation between the imide segment and the PTMO segment occurred in the composites and that there was a substantial amount of phase mixing at the same time. The formation of the silica composite had a great influence on the mobility of the segmnets in the phase-mixing domain. TGA analyses indicated that the formation of the 10 wt % silica hybrid gave a composite with a 50°C higher degradation temperature.
Chitosan interaction with soybean beta-conglycinin beta(3) was investigated by thermal unfolding experiments using CD spectroscopy. The negative ellipticity of the protein was enhanced with rising solution temperature. The transition temperature of thermal unfolding of the protein (T(m)) was 63.4 degrees C at pH 3.0 (0.15 M KCl). When chitosan was added to the protein solution, the T(m) value was elevated by 7.7 degrees C, whereas the T(m) elevation upon addition of chitosan hexamer (GlcN)(6) was 2.2 degrees C. These carbohydrates appear to interact with the protein stabilizing the protein structure, and the interaction ability could be evaluated from the T(m) elevation. Similar experiments were conducted at various pHs from 2.0 to 3.5, and the T(m) elevation was found to be enhanced in the higher pH region. We conclude that chitosan interacts with beta-conglycinin through electrostatic interactions between the positive charges of the chitosan polysaccharide and the negative charges of the protein surface.
Abstract. We demonstrate room-temperature 13C hyperpolarization by dynamic nuclear polarization (DNP) using optically polarized triplet electron spins in two polycrystalline systems: pentacene-doped [carboxyl-13C] benzoic acid and microdiamonds containing nitrogen-vacancy (NV−) centers. For both samples, the integrated solid effect (ISE) is used to polarize the 13C spin system in magnetic fields of 350–400 mT. In the benzoic acid sample, the 13C spin polarization is enhanced by up to 0.12 % through direct electron-to-13C polarization transfer without performing dynamic 1H polarization followed by 1H−13C cross-polarization. In addition, the ISE has been successfully applied to polarize naturally abundant 13C spins in a microdiamond sample to 0.01 %. To characterize the buildup of the 13C polarization, we discuss the efficiencies of direct polarization transfer between the electron and 13C spins as well as that of 13C−13C spin diffusion, examining various parameters which are beneficial or detrimental for successful bulk dynamic 13C polarization.
The kinetics of structural relaxation in Pd 42.5 Cu 30 Ni 7.5 P 20 bulk metallic glass (BMG) was investigated by means of volume relaxation and enthalpy relaxation in the temperature range below T g (µ 573 K). The measured relaxation time was significantly longer than the ¡-relaxation time reported by dynamical mechanical analysis (DMA), indicating that these two relaxation processes are fundamentally different from each other. The temperature dependence of electrical resistivity suggests that the origin of the ¢-relaxation process that occurs between room temperature and T g may be the compositional short range ordering. Anomalous volume expansion was observed in the initial stage of relaxation, which was attributed to annihilation of the p-type defects with very short relaxation time.
Woodceramics has been studied as an Ecomaterial, and is expected to have applications in a wide variety of fields. In this report, thermogravimetry and differential thermal analysis of Woodceramics with changing concentration of oxygen was conducted. Experiments in chemical reaction kinetics were also performed in order to clarify the thermo-physical and thermo-chemical properties of Woodceramics in the presence of oxygen. The experimental results show that both mass loss curves and differential heat curves are dependent on the concentration of oxygen. In addition, the reaction rate law of the thermal degradation of Woodceramics with change in concentration of oxygen is reported to verify the suitability of the method.
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