Friction and wear behavior of PI and PTFE composites for ultrasonic motors

High‐performance polymer‐based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS₂). To explore the wear mechanisms, the tribo‐pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS₂/PTFE, the AF/MoS₂/PI has much better tribological performance under high loads and speeds.     

Spherulitic growth rates and morphology of absorbable poly(p‐dioxanone) homopolymer and its copolymer by hot‐stage optical microscopy

Hot‐stage optical microscopy was used to study the crystal morphology, nucleation, and spherulitic growth rates of poly(p‐dioxanone) (PDS) homopolymer and an 89/11 PDS/glycolide segmented block copolymer. A wide range of crystallization conditions were experimentally accessible, allowing the inspection of various morphological features and accurate estimations of characteristic growth parameters, including radial growth and nucleation rates. Although the regime analysis of the crystallization kinetics indicated no breaks in the growth rate curve, the isothermal data were in excellent agreement with the Hoffman–Lauritzen theory. Spherulitic growth rates obtained from optical measurements are compared with values of the half‐time of crystallization determined earlier by differential scanning calorimetry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3073–3089, 2001     

水介质中硼酸盐-氯化镧的摩擦磨损性能研究

采用四球摩擦磨损试验机考察了硼酸钠、硼酸钾和氯化镧在水介质中的极压、抗磨和减摩性能,采用扫描电镜（SEM）、X射线能谱（EDX）、X射线光电子能谱（XPS）分析了磨斑表面形貌、主要元素的分布特征和化学状态。结果表明,硼酸钠、硼酸钾和氯化镧可一定程度地提高水的极压、抗磨和减摩性能,硼酸钾性能最优,硼酸盐与氯化镧复合后性能进一步改善。硼酸盐与氯化镧复合前摩擦表面擦伤严重,复合后擦伤明显减小,表面形成的La2O3,B2O3,Fe3O4和Fe2O3起到了良好的极压、抗磨和减摩作用。     

Structure of Modified Polytetrafluoroethylene According to DFT Calculations and 19F NMR Spectroscopy

The molecular structure of n-C₇F₁₆ and the ¹⁹F nuclear magnetic screening tensors are calculated by density functional theory (DFT) methods. The results of calculations are compared with ¹⁹F NMR data, and it is shown that fine polytetrafluoroethylene (PTFE) contains the terminal CF₃ groups in its structure.     

稀土/MoSi2复合材料的干摩擦磨损性能

运用M－2型摩擦磨损试验机测定了不同载荷条件下稀土／MoSi2复合材料与45钢配对件的干摩擦磨损性能，采用SEM观察了摩擦副表面的形貌和X射线分析了磨屑相组成，并探讨了其磨损机制。结果表明：稀土／MoSi2和MoSi2与45钢干摩擦时，在负荷不超过150N的范围内，其摩擦系数μ和磨损率W与负荷p间较好地满足关系式：W（或μ）＝a bp cp^2 p^3 ep^4，两种均具有优异的耐磨性能，在80－120N范围，稀土／MoSi2复合材料的磨损率比纯MoSi2材料的至少降低了65％；稀土／MoSi2材料的磨损机制主要是粘着磨损。     

摩擦磨损试验机模拟活塞环-缸套摩擦行为的功能开发

参考活塞环-缸套的实际运行条件,结合SRV-4摩擦磨损试验机自身的性能特点和工作原理,通过开发设计,增加合理的硬件及软件测试条件,实现摩擦磨损试验机模拟活塞环-缸套摩擦行为的功能.系统测试结果表明：功能开发后的摩擦磨损试验机可在较短时间内获得活塞环-缸套摩擦副性能优劣的试验数据,满足快速、直观评价活塞环-缸套的摩擦磨损性能的需要,在活塞环-缸套摩擦副研究中具有重要的应用价值.     

高硅SAPO-34与聚四氟乙烯复合材料的合成

以二乙胺为结构导向剂, 在聚四氟乙烯乳液中水热法合成了高硅SAPO-34与聚四氟乙烯复合材料. XRD表明合成样品为SAPO-34结构, SEM照片表明型貌完好, 周围牢固地覆盖着聚四氟乙烯材料. 与不加聚四氟乙烯乳液合成样品相比, 添加后晶粒尺寸增大, 晶型更完好, 疏水和成膜性能提高.     

稀土对镁合金AZ91D摩擦磨损性能的影响

研究了不同稀土含量对AZ91D镁合金摩擦磨损性能的影响，结果表明：在所研究的范围内，稀土镁合金的摩擦磨损特性明显优于基体合金，含与不含稀土镁合金的磨损速率都随载荷的增加而增加，磨损机制均发生了由轻微磨损向严重磨损的转变，稀土的加入细化了合金组织，改善了镁合金的综合性能，增强了磨损表面氧化膜的稳定性，提高了稀土镁合金的承载能力，有效地延迟了由轻微磨损向严重磨损的转变过程。     

Preparation and Selectivity of Molecularly Imprinted Polymer Coating on the Micro Pore Membrane of Polytetrafluoroethylene

In order to obtain mechanically stable membrane for practical application, the imprinted polymer was synthesized in the pores of polyfluoromembrane, the binding and transport ability of the membrane were studied.     

Spectroscopic Investigation of Sublimated Products of Ultradisperse Polytetrafluoroethylene

The structure of fractions isolated by thermal sublimation of ultradisperse polytetrafluoroethylene (UPTFE) powder has been studied by IR spectroscopy. At 50°C–160°C, fractions of highly amorphous fragments are condensed on a cold receiver; the fragments are constructed from branched chains with terminal olefin groups. Fractions isolated at 300°C and higher are close in structure to PTFE and are highly crystalline. It is assumed that sample amorphism is due to the irregular distribution of the fractions of fragments with terminal olefin and lateral fluoromethyl groups in the structures.Original Russian Text Copyright © 2004 by L. N. Ignatieva, A. K. Tsvetnikov, O. N. Gorbenko, T. A. Kaidalova, and V. M. Buznik__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 830–836, September–October, 2004.     

A Porous Coordination Polymer with Accessible Metal Sites and its Complementary Coordination Action

Broken switch : Guest‐accessible metal sites are generated on the pore surface of a porous coordination polymer (see figure) through the complementary coordination‐bond rearrangement in a single‐crystal‐to‐single‐crystal fashion, which is triggered by the removal of coordinated water.

     

氟化电热蒸发进样电感耦合等离子体原子发射光谱法直接测定水样和血清中铝

本文提出了一种快速、灵敏和直接测定血清和水样中痕量铝的ＩＣＰ－ＡＥＳ方法。方法基于以聚四氟乙烯为氟化剂。促进铝在石墨炉中的蒸发。研究了铝的蒸发行为，考察了共存元素的干扰，提出了铝的蒸发机理。该法测定铝的检出限为０．５ｎｇ／ｍＬ，ＲＳＤ为２．２％（ｎ＝９，Ａｌ浓度为０．２μｇ／ｍＬ），线性范围达４个数量级。采用本法直接测定了血清和自来水中的痕量铝，其分析结果和标准参考物质标定值吻合很好。     

Reversible Melting of Semi-Crystalline Polymers 2. Annealing Near to the Melting Point

Annealing experiments have been carried out at a few degrees below the melting point of different polyethylenes (LDPE, LLDPE, HDPE), of polypropylene (PP) and of Nylon-6. The heat capacities decrease during the annealing, within a 2-4 min time scale, to a lower value which corresponds to the extrapolated heat capacity values obtained for the cooling cycle when the polymer is cooled from the melt. Heat capacities in the heating cycle following the cooling cycle of PP, Nylon-6 and HDPE have the same value as during the cooling section. This is not the case for LDPE and LLDPE. Exothermic total heat flow in the cooling section following the annealing indicates that the crystallisation takes place during the cooling rather than during the annealing period. The total melting enthalpy measured before and after the annealing cycle is the same. The reversing heat flow shows an excellent fit to the change of the crystallinity measured by small angle scattering of synchrotron radiation during a heating cycle at temperatures below the melting peak. A coupled thermodynamic interaction of the crystalline and the amorphous phases is concluded from this study. This kind of interaction is possible at the lateral end of polymeric chains incorporated into the crystalline phase. This is an indication of the portion of tie molecules in the system, i.e. the portion of fringed micelle type of crystalline morphology with respect to that of folded chain lamellae. This revised version was published online in July 2006 with corrections to the Cover Date.     

Immobilization of Bovine Serum Albumin on Polytetrafluoroethylene for Application as a Potential Solid Support for Biosensor Development with Visual Detection

Immobilization of biomolecules on polymers is attractive for developing new biosensors and analytical methods. Polytetrafluoroethylene, PTFE (Teflon), is a low-cost polymer that has unique chemical and physicochemical properties. In this work, PTFE was investigated as a solid support for biosensor development. Bovine serum albumin (BSA) was immobilized directly on PTFE thin films without pretreatment. BSA was biotinylated, while the immobilization was controlled by the formation of visual spots using either streptavidin–fluorescein or streptavidin–gold nanoparticle conjugates. The visualization of the spots was accomplished by the naked eye (red spots) or a digital camera that captures the emitted fluorescence (green spots). The signal-to-background ratio was determined for both detection systems and was equal to 24.4 and 58.4 for streptavidin–fluorescein and streptavidin–gold nanoparticles, respectively.     

Segmented polyurethanes with 4,4′-bis-(6-hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI-polyurethanes in comparison with 2,4-TDI-polyurethanes

Linear segmented polyurethanes based on poly(butylene adipate)s (PBA) of different molecular weight (M_n 2000, 1000, and 600), 4,4′-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, ¹³C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA (M_n 2000) exhibit a glass transition temperature T_g of about −40°C independent of the hard segment content up to ∼50% hard segments. At higher hard segment contents increasing T_gs were observed. Polyurethanes, based on the shorter polyester soft segments PBA (M_n 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found at 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. © 1996 John Wiley & Sons, Inc.     

A novel crystalline structure - poly(tetrafluoroethylene) spherulitic crystal and its crystallization kinetics

Spherulitic crystals of Poly(tetrafluoroethylene) (PTFE), for the first time, are observed in a kind of PTFE composite, and are verified by polarized optic microscopy (POM). Differential scanning calorimetry (DSC) is used to study the isothermal crystallization kinetics of PTFE matrix at different temperatures. The result shows that Avrami parameter is near 3, which may be elucidated that PTFE crystallizes three-dimensionally from preexisting nuclei. The result is in accordance with scanning electric microscopy (SEM) and POM observation of the crystalline morphology of PTFE. Compared with the rate of one-dimension crystallization, the rate of three-dimension crystallization is lower. So the three-dimension crystallization is easier to control than the one-dimension crystallization of PTFE.     

Spherulitic growth in block copolymers and blends of miscible crystalline polymers

Spherulitic morphology and growth rate of block copolymers comprised of miscible crystalline constituents, namely poly(ethylene succinate) (PES) and poly(ethylene oxide) (PEO), were investigated. The results of the copolymers were compared with those of the blends with the same composition and molecular weight. Interpenetrating spherulites, where spherulites of one component grow in those of the other component, were observed in the copolymers as in the blends. Copolymerization, namely the connectivity of the PES and PEO blocks, reduced the spherulitic growth rate in the melt for both components. The growth inside the spherulites of the other component was discussed based on the lamellar and fibrillar (or lamella‐stack) structures, which are influenced by the interblock connectivity. Suppression of molecular mobility in the interlamellar regions resulted in the reduced nucleation and growth rate of the component growing in the spherulites of the other constituent. PES of the copolymer showed dendrites around 60 °C or above. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012