N-苯基马来酰亚胺/苯乙烯/α-甲基苯乙烯/马来酸酐四元共聚物的制备及对ABS的改性

以过氧化苯甲酰为引发剂,采用溶液聚合的方法合成了N-苯基马来酰亚胺/苯乙烯/α-甲基苯乙烯/马来酸酐四元共聚物。保持马来酸酐单体质量分数为5%,N-苯基马来酰亚胺单体质量分数为30%,改变α-甲基苯乙烯和苯乙烯的投料比合成系列四元共聚物。采用红外光谱、核磁共振和凝胶渗透色谱对四元共聚物的化学结构和相对分子质量进行了表征,考察了四元共聚物对ABS树脂耐热性及力学性能的影响。结果表明,α-甲基苯乙烯和苯乙烯的投料比为1∶1,数均相对分子质量为2.50×10~4左右的四元共聚物的玻璃化转变温度(T_g)最高达到253.3℃,5%热分解温度可达到351℃。该共聚物可使ABS共混物T_g升高到124.7℃,且具有较好的力学性能。     

HTPB/PTMEG/DADMT聚氨酯弹性体的动态性能

以端羟基聚丁二烯(HTPB)、聚四氢呋喃醚二醇(PTMEG)和2,4-甲苯二异氰酸酯(TDI-100)为原料,二甲硫基甲苯二胺(DADMT)为扩链剂,制得聚氨酯弹性体(PUE)。采用力学性能测试、差示扫描量热(DSC)、动态力学分析(DMA)及热重分析(TG)研究了HTPB/PTMEG比值、HTPB相对分子质量对PUE性能的影响。结果表明,HTPB(羟值0.836mmol/g)/PTMEG质量比为1∶4时,PUE力学性能最佳,拉伸强度30.3MPa,撕裂强度99.8kN/m;PU0(0.8)的tanδ峰位于-56.2℃,0℃以后,tanδ值低于0.08,说明丁羟型PUE比PTMEG型具有更好的动态性能,且HTPB分子量高,动态性能好;丁羟型PUE具有更高的热稳定性。     

脂肪族聚醚酯热塑性弹性体的合成与性能

本文合成了以聚丁二酸丁二醇酯(PBS)为硬段,聚四氢呋喃醚(PTMO,相对分子质量1000)为软段的生物降解脂肪族聚醚酯热塑性弹性体,其中PTMO的质量分数为50%、60%、70%。采用核磁共振氢谱、差示扫描量热法、凝胶渗透色谱、力学性能测试对嵌段共聚物的结构、熔融行为、力学性能进行了表征。结果表明:合成的目标产物为PBS/PTMO嵌段共聚物;Mn和Mw分别达到5.0×104和13.0×104以上;软段PTMO的结晶温度(Tc)较低,分别为-17.9℃、-14℃和-17.4℃;而硬段的Tc较高,分别为54.6℃和46.3℃;合成的嵌段共聚物表现出热塑性弹性体的力学行为,拉伸强度分别为22 MPa、18 MPa和14 MPa;弹性恢复率性能测试表明合成的脂肪族聚醚酯热塑性弹性体具有较好的弹性恢复性能。     

聚叠氮缩水甘油醚/聚乙二醇双软段含能聚氨酯弹性体的性能

为改善聚叠氮缩水甘油醚(GAP)的性能,以三羟甲基丙烷(TMP)为交联剂,异佛尔酮二异氰酸酯(IPDI)为固化剂,选用聚乙二醇(PEG)制备出GAP/PEG/TMP/IPDI双软段含能聚氨酯弹性体,采用红外光谱(FT-IR)、差示扫描量热(DSC)等手段进行了表征。实验结果表明,弹性体中引入聚乙二醇(PEG),拉伸强度提高168%,延伸率提高77%,所选PEG软段分子量较小,弹性体中只出现了GAP软段的Tg。随交联剂含量的增大,GAP软段的Tg由-36.85℃上升到-34.81℃,继而又下降到-40.31℃,弹性体的热分解分两段进行,初始分解温度为183℃。     

一种含能热塑性聚氨酯弹性体的性能

采用熔融二步法合成了以聚叠氮缩水甘油醚(GAP)为软段、以2,2-二叠氮甲基-1,3-丙二醇和二环已基甲烷二异氰酸酯(HMDI)为硬段的含能热塑性聚氨酯弹性体(ETPUE),通过红外光谱(FT-IR),差示扫描量热(DSC),动态力学性能测试(DMA)及力学性能测试对材料进行了结构和性能的表征.结果表明,所合成的不同硬...     

含硼多乙烯基有机硅树脂的制备及耐热性能研究

以二苯基二甲氧基硅烷、苯基三甲氧基硅烷和4-联苯硼酸为原料,采用水解-缩合的方法制备不同硼含量的苯基乙烯基杂化硅树脂预聚体(BSiR),并与含氢硅油交联剂在铂催化剂作用下硅氢加成固化得到新型的耐高温有机硅材料-聚硼硅氧烷(PBS)。采用红外光谱、核磁共振、凝胶渗透色谱、热重分析等方法对杂化硅树脂预聚体和固化物进行表征,考察了反应时间、反应温度、组分比例等因素对合成的影响。结果表明,反应温度75℃,反应时间6 h,合成硅树脂的重均相对分子质量Mw为80 246 g/mol,数均相对分子质量Mn为99 437 g/mol,分布宽度D值为1.24。以该硅树脂预聚体为基料制备的固化物在500℃下失重仅5%。     

GAP/PET聚氨酯粘合剂胶片的制备及其性能研究

为改善聚叠氮缩水甘油醚(GAP)推进剂的力学性能,选用链段柔软的环氧乙烷/四氢呋喃共聚醚(PET),采用三羟甲基丙烷(TMP)为交联剂,异佛尔酮二异氰酸酯(IPDI)为固化剂,与GAP制备聚氨酯粘合剂胶片.实验结果表明:在R为1.9,GAP:PET:TMP羟基比为1:1:3条件下,粘合剂胶片拉伸强度为3.29MPa,延伸率为625.07%.粘合剂胶片经硝化甘油/一缩二乙二醇二硝酸酯增塑后,其力学性能变化较大.在增塑比为0.5～2.1范围内,增塑胶片的Tg符合方程:Y=-77.60233+36.45135exp(-x/0.055019).     

含氢聚甲基硅氧烷的合成与表征EI北大核心CSCD

以八甲基环四硅氧烷(D4)、四甲基四氢环四硅氧烷(D4H)和六甲基二硅氧烷(MM)为原料,以强酸性离子交换树脂为催化剂,采用开环共聚法合成了一系列相对分子质量和含氢量可控、相对分子质量分布较窄的含氢聚甲基硅氧烷(PDMS-co-PHMS)。研究了催化剂种类、反应温度、反应时间、催化剂用量、搅拌速度对产物相对分子质量、含氢量以及产率的影响,并通过正交试验对工艺条件进行优化,实现了一系列具有不同含氢比例的含氢聚甲基硅氧烷的可控合成;并利用红外光谱、核磁共振和凝胶渗透色谱对产物进行分析表征。结果表明,以强酸性离子交换树脂为催化剂,可控合成了相对分子质量为1.19×103~3.01×103的含氢聚甲基硅氧烷,最佳反应条件是反应温度为60℃,反应时间为12h,催化剂质量分数为1%,搅拌速度为400 r/min。     

TLCP/SF/酚醛树脂混杂复合材料的摩擦磨损性能

采用自行合成的热致性液晶聚合物(TLCP)与酚醛树脂(PF)通过熔融挤出进行原位复合,加入经过表面处理的剑麻纤维(SF),通过辊炼、模压成型制备了TLCP/SF/PF混杂复合材料。研究液晶聚合物的种类对TLCP/SF/PF混杂复合材料摩擦磨损性能、硬度、动态力学性能的影响,使用扫描电子显微镜(SEM)观察了混杂复合材料的磨损面形貌,分析了混杂复合材料的摩擦磨损机理。研究结果表明,液晶聚合物聚对苯二甲酰-双(对羟基苯甲酸)癸二醇酯(PHDT)使TLCP/SF/PF的体积磨损率降低了15%,Tg提高了10℃。TLCP与剑麻纤维协同改善了混杂复合材料的摩擦性能,为制备无石棉摩擦材料提供理论参考。     

含氢聚甲基硅氧烷的合成与表征

以八甲基环四硅氧烷(D4)、四甲基四氢环四硅氧烷(D4H)和六甲基二硅氧烷(MM)为原料,以强酸性离子交换树脂为催化剂,采用开环共聚法合成了一系列相对分子质量和含氢量可控、相对分子质量分布较窄的含氢聚甲基硅氧烷(PDMS-co-PHMS)。研究了催化剂种类、反应温度、反应时间、催化剂用量、搅拌速度对产物相对分子质量、含氢量以及产率的影响,并通过正交试验对工艺条件进行优化,实现了一系列具有不同含氢比例的含氢聚甲基硅氧烷的可控合成;并利用红外光谱、核磁共振和凝胶渗透色谱对产物进行分析表征。结果表明,以强酸性离子交换树脂为催化剂,可控合成了相对分子质量为1.19×103~3.01×103的含氢聚甲基硅氧烷,最佳反应条件是反应温度为60℃,反应时间为12h,催化剂质量分数为1%,搅拌速度为400 r/min。     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Tc trend in high-Tc superconductors

In our previous works, we have shown that most existing ceramic superconductors can be considered to be built of superconductor-semiconductor composite and we have estimated the change in phonon spectrum of the intrinsic superconductor unit if a semiconductor unit is attached to it. Moreover, the proximity effect under the size quantization condition has been examined in the superconductor-semiconductor composite. Each of the stated effects by itself could causeT _c enhancement in general as more semiconductor blocks are added to the system. We extend our study in this paper to analyze the combined actions of phonon spectral change and proximity effect without size quantization condition onT _c variation in members of the Tl₁ series of high-T _c superconductors. Our results indicate that an optimumT _c is obtained if the stated effects are included in the idealized unit cells of the superconductors made up of a superconductor-semiconductor array.     

Anomalous Hall Effect in Sn1?x?yMnxEuyTe and Sn1?x?yMnxEryTe Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1–x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

Bulk crystalline BaPb34Bi14O3: A ceramic superconductor

The preparation conditions of the high T_C ceramic superconductor Ba(Pb,Bi)O₃ is correlated with the superconducting transition. Transition onsets of all materials are similar, but transition widths and transition completeness is strongly dependent on firing temperature. Only materials prepared over a narrow temperature range, resulting in a nearly ideal weight loss, have a complete and narrow transition.     

Electrostriction in Pb (Zn13Nb23)O3

The electrostriction in $\text{Pb (Zn}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Nb}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{)}\text{O}{}_3$ crystals has been investigated using a strain gauge method. In the ferroelectric phase below 140 C, the strain vs the electric field shows a hysteresis, which is ascribed to the effect of ferroelectric domains. A quadratic relation holds between the strain x and the electric polarization P as x = QP² above about 170 C in the paraelectric phase. Values of the electrostrictive Q coefficients are determined from the measurements near 190 C, as Q₁₁ = 1.6·10^?2m⁴/C², Q₁₂ = ?0.86·10^?2m⁴/C², and Q₄₄ = 0.85·10^?2m⁴/C².     

Effect of pressure onTc in La2-xBaxCuO4 withx=0.125

The superconducting transition temperature,T _c , of La_2–x Ba _x CuO₄ has been measured under high pressure up to 8 GPa.T _c is found to change drastically at the pressure where the structural phase transition takes place. This finding clearly indicates that there exists an intimate relation between the crystal structure and superconductivity.