原子转移自由基聚合制备PMMA/POSS杂化材料

以八(γ-氯丙基)倍半硅氧烷(OCP-POSS)为引发剂,通过原子转移自由基聚合(ATRP)制备了PMMA/OCP-POSS有机/无机杂化材料.采用GPC、DSC和TGA对杂化材料的结构与性能进行了表征.结果表明,在DMF、异丙醇、甲苯等3种不同溶剂中均可合成分子量分布较窄的PMMA杂化材料.以DMF为溶剂,所得PMMA/OCP-POSS杂化材料的分子量分布系数可达到1.18.与分子量相当的线形PMMA相比,含OCP-POSS的PMMA杂化材料具有更高的玻璃化转变温度和热稳定性.     

笼状硅氧烷低聚物/聚合物复合材料的研究进展

介绍了笼状硅氧烷低聚物（POSS）的概念、分类及其合成工艺,综述了POSS／聚合物复合材料的制备方法及其在提高聚合物在热稳定性、阻燃性能、医学性能、光电性能、形状记忆及表面性能等方面的应用。     

Liquid polyoctahedral silsesquioxanes as an effective and facile reinforcement for liquid silicone rubber

Acrylo polyoctahedral silsesquioxanes (POSS), a liquid POSS derivative with reactive C=C double bond, is used to modify addition-cured liquid silicone rubber (LSR) as an effective nanofiller for the first time. Significant enhancements on mechanical properties are obtained. With addition of only 1.5 parts per hundred rubbers (phr) of acrylo POSS to fumed silica-strengthened silicones, the Young's modulus and ultimate tensile strength are increased by 432% and 66%, respectively, and the hardness of resulting LSR composites is improved as well. Proton nuclear magnetic resonance and Fourier transform infrared spectroscopies prove the efficient hydrosilylation between Acrylo POSS and hydrosiloxane directly. The thermal stability and morphology investigations also confirm that POSS is covalently incorporated into the network of silicone rubber. The increment of crosslink density is proved by extraction and swelling experiment and dynamic mechanical analysis. It can be envisioned that this simple and effective method could help produce high performance silicone rubber composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46996.     

Phase mixture modeling of the grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics

The grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics is predicted via phase mixture modeling, using both analytical and numerical approaches. Using typical values for the thickness and properties of the grain boundaries, the equivalent volume fraction of “grain boundary phase” is calculated for a given grain shape. Based on this volume fraction estimate and a rough estimate of the grain boundary properties, the effective properties of the polycrystalline materials are calculated and compared in terms of volume-equivalent sphere diameters. For grains of cubic and tetrakaidecahedral shape excellent agreement is found between numerical calculations and analytical predictions based on the lower Hashin-Shtrikman bound. The grain size dependence is extremely weak for Young’s modulus, but can be more significant for thermal conductivity, especially when the intrinsic conductivity of the material is high. The predictions are compared to literature data.     

Bismuth layer-structured ferroelectrics with non-sheet-like polyhedral microstructures

Bismuth layer-structured ferroelectrics (BLSFs) are promising candidates for a variety of applications because of their high Curie temperature and environmentally benign nature as compared to their lead contained counterparts. Featured by the mica-like grain growth habit and spontaneous polarization along crystallographic a-b plane, it is difficult to obtain excellent ferroelectric properties for most of the BLSFs fabricated by the conventional ceramic route. Herein, a new approach is reported to obtain Bi₂WO₆ and Bi₄Ti₃O₁₂ BLSF ceramics with non-sheet-like polyhedral microstructures. The intriguing ferroelectric hysteresis behavior, dielectric tunability, and domain structures are successfully observed. The Bi₂WO₆ ceramic with a unique single-domain structure in each grain shows a typical ferroelectric polarization-electric field hysteresis loop with a remnant polarization of ~17.8 μC cm⁻² and a coercive field of ~43 kV cm⁻¹. These values have never been obtained in Bi₂WO₆ ceramics with sheet-like microstructure. The Bi₄Ti₃O₁₂ ceramic with irregular-shaped and curved tiny domains exhibits an antiferroelectric-like behavior, which is significantly different from the reported Bi₄Ti₃O₁₂ counterparts that have plate-like anisotropic grains. The present study would stimulate microstructure design and property modulation for other layer-structured materials.     

Complexity,convexity, and unimodality

A class of polygons termedunimodal is introduced. LetP = P₁,p ₂,...,p _n be a simplen-vertex polygon. Given a fixed vertex or edge, several definitions of the distance between the fixed vertex or edge and any other vertex or edge are considered. For a fixed vertex (edge), a distance measure defines a distance function as the remaining vertices (edges) are traversed in order. If for every vertex (edge) ofP a specified distance function is unimodal thenP is a unimodal polygon in the corresponding sense. Relationships between unimodal polygons, in several senses, andconvex polygons are established. Several properties are derived for unimodal polygons when the distance measure is the euclidean distance between vertices of the polygons. These properties lead to very simple 0(n) algorithms for solving a variety of problems that occur in computational geometry and pattern recognition. Furthermore, these algorithms establish that convexity is not the key factor in obtaining linear-time-complexity for solving these problems. The paper closes with several open questions in this area.     

板材凸度激光在线检测系统误差分析

本文提出了一种基于激光检测技术的高精度、稳定性好的板带凸度在线检测技术的方法,分析了该方法的XYZ三个轴方向的安装误差及同步精度对凸度测量精度的影响,对于提升我国板带生产线的测量精度和产品质量有重要意义.     

Optimal Fine and Medium Grain Parallelism Detection in Polyhedral Reduced Dependence Graphs

This paper presents an optimal algorithm for detecting line or medium grain parallelism in nested loops whose dependences are described by an approximation of distance vectors by polyhedra. In particular, this algorithm is optimal for the classical approximation by direction sectors. This result generalizes, to the case of several statements. Wolf and Lam's algorithm which is optimal for a single statement. Our algorithm relies on a dependence uniformization process and on parallelization techniques related to system of uniform recurrence equations. It can also be viewed as a combination of both Allen and Kennedy's algorithm and Wolf and Lam's algorithm.     

铝合金薄板拉伸校平工艺的研究

研究铝合金薄板新拉伸矫平工艺，解决国产薄蒙皮板不平度不符合轻型民用飞机Y12薄蒙皮平板胶接的要求，给出了关键工艺参数。