单分散聚苯乙烯颗粒的制备及其胶体晶体微球的组装

采用无皂乳液聚合技术,以过硫酸钾(KPS)为引发剂、碳酸氢钠(NaHCO3)为缓冲剂、丙烯酸(AA)为共聚单体制备了表面含羧基的单分散聚苯乙烯(PS)颗粒。用悬浮液滴蒸发自组装技术制备了三维有序胶体晶体微球。采用傅立叶变换红外光谱(FT-IR)和扫描电子显微镜(SEM)对样品结构和形貌进行表征。结果表明,聚苯乙烯颗粒粒径分布均匀,单分散性好且具有良好的球形度,丙烯酸的共聚使颗粒带有羧基而实现功能化改性。离子强度、引发剂浓度和共聚单体浓度是影响聚苯乙烯颗粒尺寸大小的重要因素。胶体晶体呈规则球形,聚苯乙烯颗粒紧密排列,形成面心立方(fcc)结构,表面表现为六方紧密有序排列。     

羧基化聚苯乙烯微球的制备及其自组装行为研究

采用分散聚合法,以乙醇、水为分散介质,苯乙烯为共聚单体,聚乙烯吡咯烷酮（PVP）为稳定剂,AIBN为引发剂,丙烯酸（AA）为功能共聚单体,制备了粒径为100—1000nm羧基化聚苯乙烯微球,研究醇水比、分散剂、引发剂用量对微球粒径及分布的影响,分析微球表面形貌、粒径分布、表面羧基含量,结果表明,胶体晶体是面心立方密排结构,微球单分散性好,表面光滑,球形度好,表面羧基含量最高可达到0．206mmol／g。同时,用垂直沉积法制备出较大范围内呈现高度有序的密排结构聚苯乙烯胶体晶体。     

氘代聚苯乙烯胶体晶体的制备及光学性质研究

以水作为介质合成了高度单分散的氘代聚苯乙烯微球,并利用垂直沉积法制备了高质量的氘代聚苯乙烯胶体晶体.傅立叶变换红外光谱清楚地表明氘代苯乙烯单体发生了聚合反应;扫描电镜表面分析展示出胶体微球的高度有序排列,断面分析表明氘代聚苯乙烯胶体晶体为面心立方结构;光学透射谱显示出氘代聚苯乙烯胶体晶体的高次布拉格衍射特征,通过和理论计算的能带结构对比,进一步证实了氘代聚苯乙烯胶体晶体为面心立方结构;变角度光学透射谱测量显示,随着入射角的增大,(111)面的衍射峰蓝移,而(200)和(220)面的衍射峰发生红移.     

单分散聚苯乙烯微球的制备及二维胶体晶体的自组装

以苯乙烯为原料、过硫酸钾为引发剂,采用无皂乳液聚合法成功地制备出具有良好球形度的单分散聚苯乙烯微球.研究了在聚苯乙烯微球合成过程中单体浓度、引发剂浓度、聚合时间对粒径及分布的影响.实验结果表明,适当改变单体浓度、引发剂浓度、聚合时间可以得到不同粒径的聚苯乙烯微球,且微球单分散性良好.采用自组装技术组装单分散聚苯乙烯微球,获得了二维有序聚苯乙烯胶体晶体.     

微米级单分散聚苯乙烯微球的制备

用分散聚合法合成2～6μm单分散好的聚苯乙烯微球,分别考察单体、稳定剂的两步加料方式,以及初始单体浓度、引发剂用量、反应温度等对所合成的聚合物微球粒径及粒径分布的影响。结果表明:两步加料方式可以显著改善微球的单分散性;随着初始单体浓度、引发剂用量增加和反应温度的升高,最终得到的聚苯乙烯微球粒径虽有所增加,但微球粒径分布变宽。将反应液体积放大、单次合成聚苯乙烯微球量不低于250g时制备出的2～6μm系列的聚苯乙烯微球,用扫描电镜等进行表征可知,所制备的聚苯乙烯微球球形度均大于0.95,相对标准偏差均小于5%。     

羧基功能化聚苯乙烯荧光微球的制备及表征

以苯乙烯、丙烯酸为单体,引入疏水性荧光染料罗丹明6G(Rh6G),采用微乳聚合法制备羧基聚苯乙烯荧光微球,并分析了表面活性剂、引发剂、丙烯酸用量对产物粒径分布的影响,考察了羧基聚苯乙烯荧光微球的浓度对荧光强度的影响。通过粒度分析仪、扫描电子显微镜、红外光谱仪、紫外吸收光谱以及荧光光谱仪对样品的纳米特性、形貌、结构和荧光性能进行了表征。结果表明,用微乳聚合法制备出50~250nm的羧基聚苯乙烯荧光微球,粒径均一且呈单分散性。紫外光谱图测试表明,在533nm左右有吸收峰。荧光光谱测试表明,羧基功能化的荧光聚苯乙烯微球浓度≤0.01%,其荧光最大激发峰为527nm,最大发射峰在555nm处;浓度高于0.01%时,荧光光谱出现红移,且荧光强度减弱。     

无皂乳液聚合法制备单分散聚苯乙烯微球

以苯乙烯(St)为单体,过硫酸钾(KPS)为引发剂,采用无皂乳液聚合法制备了聚苯乙烯微球。研究了单体、引发剂的浓度,引发剂加入方式,聚合温度对制备PS微球粒径的影响。运用傅立叶红外光谱(FT-IR)、透射电子显微镜(TEM)、场发射扫描电镜(FE-SEM)、电势与纳米粒径分析仪等手段,对微球的组成成分、表面形态、粒径及其分布、表面电势进行了表征。结果表明微球粒径均匀,在100～200nm范围内,球形度良好且呈单分散性。     

种子溶胀聚合法制备微米级聚苯乙烯微球

以分散聚合法制备的平均粒径为7.7μm的聚苯乙烯微球为种子,与溶胀剂和单体、引发剂的混合物经二步溶胀聚合法溶胀聚合后,制备大粒径单分散聚苯乙烯微球,并讨论溶胀剂的种类、溶胀剂用量、单体用量、单体和引发剂的加入方式、溶胀温度等因素对聚苯乙烯微球粒径及单分散性的影响。结果表明:当邻苯二甲酸二丁酯与聚苯乙烯种子的质量比为7,单体与聚苯乙烯种子质量比为9,且引发剂与单体同时加入,溶胀温度30℃时,可制得平均粒径为12.2μm左右且单分散性较好的聚苯乙烯微球。     

聚苯乙烯微球的研究进展

简要介绍并比较了聚苯乙烯微球的各种制备方法，着重讨论了制备聚苯乙烯微球时反应体系中单体、引发剂、分散剂、反应介质等对微球粒径及粒径分布的影响。这为制备单分散性、粒径可控的聚苯乙烯微球奠定了基础。     

一步法制备两亲性不对称微球

首先以苯乙烯为单体,十二烷基磺酸钠(SDS)为乳化剂,二乙烯基苯(DVB)为交联剂,十六烷(HD)为助稳定剂,分别以偶氮二异丁腈(AIBN)、过硫酸钾为引发剂通过乳液聚合法制备出非球形聚苯乙烯微球。在聚合反应1.5 h后以偶氮二异丁腈为引发剂时通过滴加第二单体丙烯酰胺,在聚苯乙烯与水相界面处继续引发丙烯酰胺聚合一步制备出两亲性不对称微球。同时探究了乳化剂用量和原料配比对非球形聚苯乙烯微球形貌的影响。测试结果表明,采用油溶性引发剂时聚苯乙烯微球边缘的突起部分随着阴离子型乳化剂SDS含量的增加而减小;采用水溶性引发剂时聚苯乙烯微球外边缘的表面弧度随着苯乙烯单体与液态石蜡质量比的增加而逐渐增大,从帽檐形状渐变为碗状。     

Kinks in the a/2〈111〉 screw dislocation in Ta

We study the structure and formation energy of kinks in the 1/2a〈111〉 screw dislocations in metallic Tantalum (Ta) using molecular dynamics with a first principles based many-body interatomic potential. In our study, four a/3〈112〉 kinks are constructed in a quadrupole arrangement in the simulation cell. To the simulation cell, we impose periodic boundary conditions in the directions perpendicular to the [111] direction and fix boundary condition in the [111] direction. We find that two, energetically equivalent, core configurations for the 1/2a〈111〈 dislocation lead to 8 distinguishable single kinks and 16 kinds of kink pairs. The different mismatches of the core configurations along [111] direction attributed to the differences in the formation energy for various types of kinks. Formation energies for all possible kinds of isolated single kinks and kink pairs have been determined. It was found that 0.730 eV was the lowest energy cost to form a kink pair in the a/2〈111〉: screw dislocation in Ta.     

Orientation,twinning and orientation-dependent reflectance in InSb-GaSb alloys

InSb-GaSb solid solution ingots prepared by directional solidification aboard Skylab and on earth consist primarily of twins with (111) twin planes parallel to the direction of solidification and growth directions that lie along 〈211〉, 〈110〉, or 〈321〉 crystallographic directions.The optical bireflectance exhibited by polished samples when observed by reflected plane-polarized white light is symmetrical with respect to twin boundaries, regardless of twin orientation relative to solidification direction, and displays a two-fold rotational symmetry rather than the four-fold symmetry normally associated with uniaxial strain birefringence.     

Fatigue striation formation in an Fe–3%Si alloy—effects of crystallographic orientation and neighbouring grains

In order to know the criterion of fatigue striation formation, fatigue fracture surfaces and crack paths were investigated in Fe–3%Si single and bicrystals having various crystallographic orientations. On single crystals, striations were formed when the loading direction was close to a 〈110〉 direction. In this direction, the crack grew perpendicular to the loading direction. When the loading direction was near a 〈111〉 direction and the crack grew along an inclined plane, no striations were observed. Even in this orientation, when the crack grew perpendicular by necessity using bicrystals, striations were observed. This suggests that striations are not formed on a special crystallographic plane, but are formed when the fatigue crack plane is perpendicular to the loading direction regardless of crystallographic orientation.     

光引发淀粉-AM/AA反相乳液接枝聚合--光引发剂的影响

采用多种光引发剂引发淀粉-丙烯酰胺/丙烯酸反相乳液接枝聚合,IR光谱分析表明了淀粉接枝共聚物的生成,考察了光引发剂的种类和浓度对接枝聚合的影响并初步探讨了引发接枝的机理。     

Textures of tantalum metal sheets by neutron diffraction

The orientation distributions of six tantalum samples, TaPA, TaG1, TaG2, TaQ2-S1, TaQ2-S2 and TaQ2-S4, were studied by neutron diffraction and ODF analysis. The TaPA specimen is a commercial tantalum sheet with an unknown fabrication history. The TaG1 and TaG2 were fabricated from a powder metallurgical ingot by uniaxial compression, and the TaQ2 type samples were fabricated from commercial stock by similar uniaxial forging. TaQ2-S1 is the section closest to the centre of the forged disc, S2 is the intermediate section, and S4 is the section adjacent to the periphery. The texture of TaPA consisted of many components, including {014}〈100〉, {111}〈ˉ321〉, {100}〈010〉, and [111]/[100] double-fibre textures with the fibre axes oriented parallel to the normal direction. The two TaG-type specimens were dominated by the [111]/[100] double-fibre texture, accompanied by a weak {100}〈010〉 cube texture. The three sections of TaQ2 had much higher degrees of texture than the TaG-type samples, with an extremely strong (111) peak, which consists of (111)〈11ˉ2〉, (111) 〈ˉ1ˉ12〉, and [111] fibre texture. The average pole density of the three equivalent orientations of (111)〈11ˉ2〉 was the strongest for the S1 with over 150 multiples of random distribution (mrd), and gradually decreased with increasing radial distance to about 100 mrd for the S4 section. On the other hand, the average intensity of (111)〈ˉ1ˉ12〉 type orientations was increased from about 40 mrd at S1 to about 100 mrd for the S4 section.     

二氧化氮引发丙烯酸聚合反应动力学

在二氧化氮引发下完成了丙烯酸的聚合反应，研究了引发剂的浓度、单体浓度及温度对聚合反应的影响，求出聚合反应的表现活化能为35kJ／mol，测定了聚合物的特性粘度，计算出聚合物的平均分子量，提出了聚合反应为自由基历程。     

Enhancing effect of substrate bias on nanotwin formation of sputtered Ag thin films

In this study, a novel method for producing high-density 〈111〉-oriented nanotwinned Ag film is proposed so as to improve the performance of backside metallization for power devices. Negative bias voltages were applied during sputtering to facilitate the formation of densely stacked nanotwinned columnar structures. In addition, the effects of substrate bias on the properties of Ag films were observed in the lower transition layer thickness, stronger 〈111〉 texture, and higher indentation hardness. The optimal indentation hardness, 1.71 GPa, was found in the nanotwinned Ag film sputtered with a bias voltage of???150 V; it was about twice that of the normal-grained Ag film sputtered without substrate bias, 0.85 GPa. In addition, the results showed that the Ag film sputtered with a bias voltage of???150 V possessed the strongest (111) intensity, and its surface (111) ratio was 98%, much higher than the 77% of the Ag film sputtered without substrate bias. It is concluded that the Ag nanotwinned film sputtered with a bias voltage of???150 V has the potential for application as an interlayer in low-temperature direct bonding.

     

Biaxially textured Ag films by grazing ion beam assisted deposition

The effect of grazing incidence 4 keV Ar⁺ ion irradiation on the early stage of Ag thin film growth on amorphous Si was investigated. The double effect of axial and surface channeling resulted in grains oriented along the 〈110〉 axis in-plane, while the (111) out-of-plane texture was maintained. A slight average tilt of the (111) out-of-plane texture axis towards the ion beam direction is proposed to result from the difference between terrace and step edge sputtering yield. The observed tilt is consistent with a minimum erosion orientation of the surface profile.     

Anisotropic crystallite size analysis of textured nanocrystalline silicon thin films probed by X-ray diffraction

A newly developed X-ray technique is used, which is able to quantitatively combine texture, structure, anisotropic crystallite shape and film thickness analyses of nanocrystalline silicon films. The films are grown by reactive magnetron sputtering in a plasma mixture of H₂ and Ar onto amorphous SiO₂ and single-crystal (100)-Si substrates. Whatever the used substrate, preferred orientations are observed with texture strengths around 2-3 times a random distribution, with a tendency to achieve lower strengths for films grown on SiO₂ substrates. As a global trend, anisotropic shapes and textures are correlated with longest crystallite sizes along the 〈111〉 direction but absence of 〈111〉 oriented crystallites. Cell parameters are systematically observed larger than the value for bulk silicon, by approximately 0.005-0.015 Å.     

Fracture toughness measurement of thin-film silicon

The fracture toughness of single‐crystal silicon thin films oriented to (100) and (110) was investigated by tensile testing under both 〈100〉 and 〈110〉 loading conditions. The specimen was fabricated from a p‐type Czochralski (CZ)‐grown wafer and passed through a thermal process during the fabrication of the test device. The measured fracture toughness is dependent on the loading direction in the tensile test and independent of the specimen surface orientation. The test results were 1.94 MPa√m in the 〈100〉 direction and 1.17 MPa√m in the 〈110〉. In these tests, no longitudinal size effect on the fracture stress or fracture toughness was observed. The SEM photographs obtained from the fracture specimens after the tensile test show that the crack initiated from the notch tip and propagated straight in the across‐the‐width direction on the (110) or (111) cleavage plane.