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101.
S. Piril Ertem Emel Yilgor Cagla Kosak Garth L. Wilkes Mingqiang Zhang Iskender Yilgor 《Polymer》2012,53(21):4614-4622
Influence of soft segment molecular weight and hard segment content on the morphology, thermomechanical and tensile properties of homologous polyurethaneurea copolymers based on narrow molecular weight poly(propylene oxide)glycol (PPG) oligomers were investigated. A series of polyurethaneureas with hard segment contents of 12–45% by weight and PPG number average molecular weights <Mn> of 2000 to 11,800 g/mol were synthesized and characterized structurally by SAXS and mechanically by DMA and stress strain analysis. Bis(4-isocyanatocyclohexyl)methane and 2-methyl-1,5-diaminopentane were used as the diisocyanate and the chain extender respectively. All copolymers displayed microphase separation by SAXS and DMA. The critical entanglement molecular weight (Me) of PPG is reported to be around 7700 g/mol. Our mechanical results suggest that when copolymers possess similar hard segment contents and are compared to those based on soft segments with number average molecular weights (Mn) greater than Me, they generally displayed higher tensile strengths and particularly lower hysteresis and creep than those having soft segment molecular weights below Me. These results imply that soft segment entanglements in thermoplastic polyurethaneureas may provide a critical contribution to the tensile properties of these copolymers – particularly in the range where the soft segment content is dominant. 相似文献
102.
Invertase was immobilized into polyacrylamide–gelatin carrier system by chemical cross-linking with chromium (III) acetate, chromium (III) sulphate, and potassium chromium (III) sulphate. The optimum conditions, namely substrate concentration, temperature, and pH were determined. The effect of polyacrylamide–gelatin ratio and cross-linker concentration on immobilized enzyme activity were analysed. Maximum immobilized enzyme activities were obtained with chromium (III) acetate (0.01 mol dm−3), chromium (III) sulphate (0.004 mol dm−3) and potassium chromium (III) sulphate (0.001 mol dm−3) for 0.177 (w/w) polyacrylamide–gelatin carrier ratio as 79%, 72% and 79%, respectively. The Km values were 86 and 166 mM for free and immobilized enzyme, respectively. All immobilized samples were used 20 times over a period of 2 months without a considerable loss of activity. 相似文献
103.
Effect of polydimethylsiloxane (PDMS) soft segment molecular weight (Mn = 3200, 10,800 and 31,500 g/mol) and urea hard segment content (2.0-11.4% by weight) on the hysteresis and permanent set behavior of segmented silicone-urea (TPSU) copolymers were investigated. In spite of very low hard segment contents, all copolymers formed self-supporting films and displayed good mechanical properties. When the mechanical hysteresis and set behavior of the silicone-urea copolymers with similar hard segment contents (around 7.5% by weight) but based on PDMS-3K, PDMS-11K and PDMS-32K were compared, it was very clear that as the PDMS molecular weight increased, hysteresis and instantaneous set values decreased significantly. Copolymers based on the same silicone soft segment (PDMS-11K or PDMS-32K) but with different hard segment contents showed a linear increase in hysteresis and a slight decrease in the instantaneous set as a function of hard segment content. Constant initial stress creep experiments also showed lower creep as the PDMS segment molecular weight increased for copolymers with similar urea contents. Since the critical entanglement molecular weight (Me) of PDMS is stated to be 24,500 g/mol, our results tend to suggest important contribution of chain entanglements on the hysteresis and instantaneous set of these silicone-urea copolymers. 相似文献
104.
Nanocomposites consisting of thermoplastic polyurethane–urea (TPU) and silica nanoparticles of various size and filler loadings were prepared by solution blending and extensively characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), thermal analysis, tensile tests, and nanoindentation. TPU copolymer was based on a cycloaliphatic diisocyanate and poly(tetramethylene oxide) (PTMO-2000) soft segments and had urea hard segment content of 20% by weight. TPU/silica nanocomposites using silica particles of different size (29, 74 and 215 nm) and at different loadings (1, 5, 10, 20 and 40 wt. %) were prepared and characterized. Solution blending using isopropyl alcohol resulted in even distribution of silica nanoparticles in the polyurethane–urea matrix. FTIR spectroscopy indicated strong interactions between silica particles and polyether segments. Incorporation of silica nanoparticles of smaller size led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. Increased filler content of up to about 20 wt. % resulted in materials with higher elastic moduli and tensile strength while the glass transition temperature remained the same. The fracture toughness increased relative to neat TPU regardless of the silica particle size. Improvements in tensile properties of the nanocomposites, particularly at intermediate silica loading levels and smaller particle size, are attributed to the interactions between the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers. 相似文献
105.
A. N. Gruzintsev G. A. Emel’chenko V. M. Masalov E. E. Yakimov 《Inorganic Materials》2009,45(3):260-263
We have studied the effect of the stop band and coupled photonic modes on the visible luminescence of synthetic opal photonic crystals. The results demonstrate that the position of the photonic stop band in the luminescence spectrum of opal depends on the nanosphere diameter. Optical measurements have been used to determine the refractive index of the photonic crystals and the silica sphere diameter. We have assessed the effect of coupled modes in opal on its intrinsic luminescence spectrum. Coupled modes of visible light in opal can be visualized by applying a matte sapphire plate to the opal surface. 相似文献
106.
Bismuth nano-Hall probes with dimensions ~120 × 120 nm were fabricated by focused ion beam milling and used for the direct room temperature magnetic imaging of crystalline garnet thin films and strontium ferrite permanent magnets by scanning Hall probe microscopy. At driving currents of 40 μA, the Hall coefficient and magnetic field sensitivity of the Bi nano-Hall probes were 3.3 × 10-4 Ω/G and 7.2 G/√Hz, respectively 相似文献
107.
Musharaf Muhammad Karamat Shumaila Hassan Muhammad Umair Khalique Uzma Oral Ahmet Behjat Arash Badami Akram Rizwan Almohaimeed Ziyad 《Journal of Superconductivity and Novel Magnetism》2021,34(10):2633-2642
Journal of Superconductivity and Novel Magnetism - Crystalline ZnO offers an excellent host matrix to create a dilute magnetic semiconductor (DMS) owing to its facile Zn-atom substitution with the... 相似文献
108.
The structure of full-scale simulators of nuclear power plants and their development are described. The special features of
analytical simulators, which are economical tools for training nuclear power plant personnel because they require only a small
investment of capital, are described. An industrial technology for developing simulators for nuclear power plants has been
adopted and is maintained at a modern level at the All-Russia Scientific-Research Institute of Nuclear Power Plants. A change
in the technical policy of the concern Rosénergoatom made it possible to solve, by and large, the problem of equipping nuclear
power plants in Russia with simulators. 3 figures, 1 table, 4 references.
All-Russia Scientific-Research Institute of Nuclear Power Plants. Translated from Atomnaya énergiya, Vol. 88, No. 6. pp. 407–414,
June, 2000. 相似文献
109.
Main purpose of this project is to develop fundamental technology for assist robots to recover and maintain human motor skill and to extend scope of human activity. Our goal is to provide a system that adapts to its user’s personal behavior patterns in real-time. We aim to develop a continuous collaboration system between the assist robots and the user where both alternatively adjust to each other to maximize the system’s utility. To understand human movement, we recorded motion sequence of several tasks for different subjects using motion capture system. Through analysis of human motion data, we extracted a general model by rule-based approach. On the other hand, since such tasks are not feasible with static models, we investigate the potential benefit of supervised online learning in the task of online action classi?cation and Deep Learning in the task of acquiring human motion. Finally, developed system was extended to show its potential effect in ergonomics and in assist robotics. 相似文献
110.
Ziyatdinov N. N. Emel’yanov I. I. Tuen Le Quang 《Theoretical Foundations of Chemical Engineering》2018,52(6):943-955
Theoretical Foundations of Chemical Engineering - A new algorithmic approach to the synthesis of economically optimum multistage heat exchange network in the design and reconstruction of... 相似文献