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991.
以TiCl4为原料,采用低温液相水解法制备了纳米TiO2粉体,着重研究了Ti4 的浓度和添加聚乙烯吡咯烷酮(Polyvinylpyrrolidone,PVP)对产物的晶相、颗粒大小和表面形貌的影响.使用XRD,TEM,SEM,激光粒度测试仪对样品进行了表征.结果表明,Ti4 浓度影响TiO2粉体的相转变温度,随着Ti4 浓度的升高金红石相的含量逐渐升高,但粉体分散性变差;添加PVP提高了所得TiO2粉体的分散性,粒径降低为40~50 nm左右,并改善了粉体的形貌. 相似文献
992.
Narrowly distributed nanoparticles of poly (n‐butyl methacrylate‐co‐vinyl pyrrolidone) were prepared through microemulsion polymerization with a nonionic surfactant of Tween‐80 as emulsifier (6 wt % of the latex) and n‐butanol as coemulsifier. The polymerizations were initiated with benzoylperoxide (BPO), potassium persulfate (KPS), KPS/ferric sulfate (FeSO4), and BPO/FeSO4, respectively, where the initiation in the case of BPO/FeSO4 took place mainly at the interphase between the oil phase and the reaction media. Namely, this interfacial‐initiated microemulsion polymerization resulted in larger particles with relatively narrower particle size distribution as well as higher limiting monomer conversion but lower polymerization rate compared with the polymerization initiated with KPS/FeSO4. In this article, the influences of initiation method, monomer ratio, and addition of water‐soluble components on microemulsion polymerization and latex particle size were studied to discuss the mechanism of interfacial‐initiated microemulsion polymerization. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2334–2340, 2004 相似文献
993.
The preparation of near stoichiometric spinel and alumina-rich spinel composites from Al2 O3 and MgO powders with the addition of Na3 AlF6 up to 4 wt% in the temperature range 700°–1600°C was studied; 98 wt% spinel containing 72 wt% Al2 O3 can be produced from the mixture of 72 wt% (50 at.%) Al2 O3 + 28 wt% (50 at.%) MgO powders with the addition of 1 wt% Na3 AlF6 fired at 1300°C for 1 h. Spinels containing 81–85 wt% Al2 O3 can be produced from either the mixture of 90 wt% (78 at.%) Al2 O3 + 10 wt% (22 at.%) MgO or the mixture of 95 wt% (88 at.%) Al2 O3 + 5 wt% (12 at.%) MgO powders with the addition of 4 wt% Na3 AlF6 in the temperature range 1300°–1600°C by using a torch-flame firing for 3 min, followed by quenching in water, while the same system under slow cooling in a furnace results in spinel containing 74–76 wt% Al2 O3 . Microscopic studies indicate that the alumina-rich spinel composites consist of a continuous majority spinel phase and an isolated minority corundum phase, regardless of slow cooling in a furnace or quenching in water. 相似文献
994.
端氨基聚脲聚氨酯环氧树脂体系的固化反应及粘接性能 总被引:2,自引:0,他引:2
本文采用DTA和FT-IR研究了端氨基聚脲聚氨酯固化环氧树脂的反应特性,考察了被粘表面状态、偶联剂和促进剂、填料等对剪切强度性能的影响。并对该粘合剂耐化学腐蚀性进行了试验,说明具有好的耐腐蚀性。 相似文献
995.
Three types of pegylated amphiphilic copolymers of poly(δ‐valerolactone) (PVL) were copolymerized with methoxy poly(ethylene glycol) (MePEG) and poly(ethylene glycol) (PEG4000 and PEG10,000), respectively. Pegylation of PVL allowed copolymers possessing amphiphilic property and efficiently self‐assembled to form micelles with a low critical micelle concentration (CMC) in the range of 10?7–10?8M. The average molecular weight of copolymers was in the range of 10,000–20,000 Da, and the polydispersity of copolymers was about 1.7–1.8. Higher mobility of low molecular weight PEG (i.e., MePEG and PEG4000) than high molecular weight PEG10,000 allowed valerolactone ring opening more efficient in terms of PVL/MePEG and PVL/PEG4000 copolymers possessing longer chain length in hydrophobic domain. Pegylated PVL with low CMC and triblock structure was preferred to encapsulate drug during micelle formation. Although all of these amphiphilic copolymers exhibited controlled release character, the micelles formed by triblock copolymer possessed a more stable core‐shell conformation than that by diblock copolymer, and resulted in the release of drug from triblock micelles slower than that from diblock micelles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1836–1841, 2006 相似文献
996.
Y. F. Zhou S. Xie X. W. Ge C. H. Chen K. Amine 《Journal of Applied Electrochemistry》2004,34(11):1119-1125
An admixture of commercial liquid electrolyte (LB302, 1 M solution of LiPF6 in 1:1 EC/DEC) and methyl methacrylate (MMA) was enclosed in CR2032 cells. The assembled cells were then -ray-irradiated using configurations of half cells and full cells. Through this in situ irradiation polymerization process, we obtained rechargeable lithium ion cells with poly(methyl methacrylate) (PMMA) based gel polymer electrolytes (GPE). Galvanostatic cycling, AC impedance spectroscopy, and cyclic voltammetry were employed to investigate the electrochemical properties of the cells and the gel polymer electrolyte. This PMMA-based gel polymer electrolyte was found to exhibit a high ionic conductivity (at least 10–3 S cm–1) at room temperature. Due to a significant increase in the charge transfer resistance between the GPE and the cathode, the cell impedance of a PMMA-based lithium ion cell is greater than that of a liquid-electrolyte-based cell. The discharge capacity of a LiNi0.8Co0.2O2/GPE/graphite is approximately 145 mAh g–1 for the first cycle and decreases to123 mAh g–1 after 20 cycles. In addition, a large initial cell impedance (LICI) was observed in the irradiated positive half cell. In this paper, we propose a possible mechanism related to the detachment of the PMMA layer from the lithium electrode. This detachment of the PMMA layer from the lithium electrode has not been explicitly discussed previously. 相似文献
997.
Hydrolysis of olive oil, soybean oil, mink fat, lard, palm oil, coconut oil, and a hydrogenated, hardened oil with lipase
from anAspergillus sp. has been studied. The lipase had high specific activity (60,000 U/g) and did not show any positional specificity. The
lipase proved to be a more effective catalyst than Lipolase fromA. oryzae, with an optimal activity at 37°C and pH 6.5–7.0. It was activated by Ca2+ but inactivated by organic solvents such as isopropanol and propanone. All substrates examined could be hydrolyzed to corresponding
fatty acids with this enzyme at concentrations of 5–30 U/meq with yields of 90–99% in 2–24 h. The degree of hydrolysis was
almost logarithmically linear with reaction time and occurred in two stages. The lipase was stable and could be repeatedly
recycled for hydrolysis. 相似文献
998.
Lin C.H.; Chan F.C.H.; Hwang J.K.; Lyu P.C. 《Protein engineering, design & selection : PEDS》1999,12(7):589-595
Conantokin-T (con-T) and conantokin-G (con-G) are two highlyhomologous peptide toxins found in Conus venom. The former isa 21-residue peptide with four -carboxyglutamic acid (Gla) residues(at positions 3, 4, 10 and 14), while the latter is a 17-residuepeptide with five -carboxyglutamic acid residues (at positions3, 4, 7, 10 and 14). Despite the apparent similarity in numberand relative positions of the -carboxyglutamic acid residues,113Cd-NMR studies indicated a distinct metal binding behaviorfor con-G and con-T. There appears to be four binding sitesin con-G in contrast to one metal binding site in con-T. Toelucidate the mode of calcium binding by the -carboxyglutamicacid residues in these conantokins, we designed various analogouspeptides with their -carboxyglutamic acid replaced by otheramino acid residues. 113Cd-NMR experiments on conantokin analoguesreveal that the major difference in the number of metal bindingsites between con-G and con-T is due to the residue at position7. We also performed molecular simulations to calculate therelative binding free energies of several potential bindingsites. Based on our theoretical and experimental results, wepropose a `four-site' binding model for conantokin-G and a `single-site'binding model for conantokin-T. 相似文献
999.
Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007 相似文献
1000.
Polymer peroxides were synthesized by copolymerizing tert‐butyl‐3‐isopropenylcumylperoxide (D‐120) with styrene (St). Exothermic peak at 192.7°C in DSC thermogram indicated that peroxy bonds in D‐120 remained intact during the copolymerizing process. The polymeric peroxide was used to initiate polymerization of St. GPC results showed that polystyrene (PS) initiated by the polymeric peroxides was composed of both linear and branched molecules. In addition, the rheology test showed that PS samples initiated by polymeric peroxide contained branched structure and had lower shear viscosities. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 197–202, 2006 相似文献