Boundary lubrication under water

Boundary lubrication, in which the rubbing surfaces are coated with molecular monolayers, has been studied extensively for over half a century. Such monolayers generally consist of amphiphilic surfactants anchored by their polar headgroups; sliding occurs at the interface between the layers, greatly reducing friction and especially wear of the underlying substrates. This process, widespread in engineering applications, is also predicted to occur in biological lubrication via phospholipid films, though few systematic studies on friction between surfactant layers in aqueous environments have been carried out. Here we show that the frictional stress between two sliding surfaces bearing surfactant monolayers may decrease, when immersed in water, to as little as one per cent or less of its value in air (or oil). We attribute this to the shift of the slip plane from between the surfactant layers, to the surfactant/substrate interface. The low friction would then be due to the fluid hydration layers surrounding the polar head groups attached to the substrate. These results may have implications for future technological and biomedical applications.     

表面诱导开环聚合制备聚合物刷的实验

针对通过反应时间调控聚合反应在室温条件下硅基表面的聚合物薄膜厚度问题,采用表面诱导活性开环聚合的方法,以N-己基-5-降冰片烯-2,5-二羧酰亚胺为聚合单体,通过对聚合催化剂的筛选,确定使用Grubbs二代催化剂,进行聚合物刷制备的实验研究.实验结果表明:通过表面诱导活性开环聚合,把聚合物通过化学键连接到基板表面,获得了厚度超过100 nm、表面光滑的、大面积生长的纳米级聚合物刷.研究结果对采用表面诱导开环聚合方法制备出高质量的聚合物刷有非常重要的理论意义和实用价值.     

Anisotropic spinodal dewetting as a route to self-assembly of patterned surfaces

The ability to pattern surfaces on a microscopic length scale is of importance for technological applications such as the fabrication of microelectronic circuits and digital storage media. Devices fabricated entirely from polymers are now available, opening up the possibility of adapting polymer processing technologies to fabricate cheap, large-area devices using non-lithographic techniques--for example, by exploiting dewetting and phase separation in thin films. But the final pattern adopted by the polymer film using such approaches requires a template printed onto the substrate by optical lithography, microcontact printing or vapour deposition. Here we describe a simple process for patterning surfaces that does not require a template. Our method involves the spinodal dewetting of a polymer surface by a thin polymer film, in which a liquid film breaks up owing to the amplification of thermal fluctuations in film thickness induced by dispersion forces. A preferred orientation is imposed on the dewetting process simply by rubbing the substrate, and this gives rise to patterns of remarkably well-aligned polymer lines. The width of these lines is well-defined, and is controlled by the magnitude of the dispersion forces at the interface, which in turn can be varied by varying the thickness of the polymer substrate. We expect that further work will make it possible to optimize the degree of order in the final morphology.     

γ射线辐照尼龙1010的磨擦学特性

用剂量为80kGy及120kGy的γ射线分别对尼龙1010进行辐照改性，以淬火45^#钢为环试样分别与辐照及未辐照的尼龙1010块试样组成摩擦副，在MM-200环-块磨擦试验机上评价它们在干摩擦、水润滑及油润滑条件下的摩擦磨损行为。用光学金相显微镜观察辐照及未辐照样品磨损后的表面形貌。研究结果发现：γ射线辐照提高了PA1010的干摩擦及油润滑耐磨性能，且辐照剂量越大，耐磨性越好。水润滑条件下，在10kg的低栽下，80kGy剂量辐照的样品耐磨性最好，而20kg的高载下，2个剂量辐照后的样品耐磨性都变差了。     

聚氨酯橡胶和丁腈橡胶-镍基喷焊层摩擦副湿磨粒磨损试验研究

对聚氨酯橡胶(UR)丁腈橡胶(NBR)与Ni基喷焊层摩擦副湿磨粒磨损进行了试验研究。研究结果表明,摩擦副具有较强的抗磨性,聚氨酯橡胶(UR)较丁腈橡胶(NBR)具有更高的抗磨性。高聚物的磨损量随比压和相对速度的增加而增大,摩擦系数随相对速度的增加而增大,随比压的增加而减少。本试验结果对石油钻井机械中,摩擦副在磨粒、腐蚀介质中的选材有参考价值。     

基于热力耦合的摩擦系数计算模型与仿真研究

基于界面摩擦过程中摩擦功耗散为界面原子热振动的原理,通过对界面原子在界面势能场激励作用下热振动分析,建立了基于摩擦界面热力耦合过程的滑动摩擦系数计算模型。仿真分析表明：滑动摩擦系数随摩擦速度增加而增高;当摩擦界面实际接触面积与载荷成线性关系时,摩擦系数与接触面积无关,当实际接触面积接近名义接触面积时,摩擦系数随载荷的增加而降低;此外,滑动摩擦系数随晶格常数增大而降低,随原子质量减小而升高。     

预氧化、预滑动在磨损过程中的作用

用中ＣｕＣｒＭｏ和４Ｃｒ９Ｓｉ２作为摩擦副,在无润滑条件下进行滑动磨损试验,通过预氧化、预滑动在摩擦副表面预先形成氧化物,研究其在磨损过程中的作用结果表明,预氧化、预滑动能缩短随后滑动中的磨合期,减小最初严重磨损,且由于预滑动、预氧化形成的氧化物形态不同,预滑动的减磨作用更为明显;预滑动还能减小随后在较高环境温度下滑动的磨损从预氧化、预滑动的作用可知,形成致密的氧化层对于减小磨损是非常必要的所以,通过预氧化、预滑动可以使其它磨损形态转化为氧化磨损,从而减小磨损速率,达到减轻磨损的目的     

高铬铸铁丁腈橡胶的摩擦磨损性能试验研究(一)

本文介绍了不同硬度,不同光洁度的高铬铸铁试环对磨不同硬度的丁腈橡胶试块的摩擦磨损性能,试验研究作出了环与块间的摩擦系数和滑动速度关系曲线(f—n曲线)和三组不同材料硬度,不同光洁度匹配情况下的磨损曲线。初步得出了高铬铸铁材料硬度、光洁度与丁腈橡胶材料硬度的合理匹配值。     

Synthesis,characterization, and tunable wettability of poly(ionic liquid) brushes via nitroxide-mediated radical polymerization (NMP)

Well-defined poly (ionic liquid) brushes with tunable wettability are successfully synthesized via nitroxide-mediated radical polymerization. X-ray photoelectron spectroscopy, attenuated total reflection infrared spectroscopy and static water contact angle measurements are used to monitor each step. Ellipsometry, nuclear magnetic resonance (1H and 13C) spectra and gel permeation chromatographic measurements reveal that there is a linear increase in polymer film thickness with polymerization time, indicating that chain growth from the surface is a controlled/“living” polymerization. The surface morphology was measured by atomic force microscopy. Moreover, the surfaces of the poly (ionic liquid) brushes with tunable wettability and reversible switching between hydrophilicity and hydrophobicity can be easily achieved by counteranion exchange.     

录音磁头在实用条件下的摩擦学性能

在实际使用条件下,研究了三种坡莫合金录音磁头的摩擦学性能。研究了磁头磨损参数随使用时间的变化规律,以及磁头不同铁芯和屏蔽罩材料对磁头摩擦学性能的影响,比较了不同磁带运行速度下磁头的磨损行为,并进行了磁头的磨损失效分析。结果表明,录音磁头表面磨损为不均匀磨损,随磨损时间延长不均匀磨损更严重;三种磁头因铁芯、屏蔽罩材料不同而具有不同的摩擦学性能,其中硬坡莫合金磁头耐磨性能最好;磁头磨损是由于从磁带上脱落的Ｆｅ２Ｏ３磁粉颗粒的微切削作用造成磁头表面划痕;磁头在磨损过程中表层有冷加工硬化现象。     

纳观纹理表面往复滑动接触磨损问题研究进展

纳米器件滑动接触过程中,由于黏附磨损而很快失效,很难应用于工程实际。表面纹理通过降低比表面来减小磨损,在往复滑动接触过程中,伴随着材料的迁移,接触条件不断更新,使得往复滑动接触磨损问题的研究变的更加困难。为此,对观纹理表面往复滑动接触磨损问题的试验研究和数值模拟研究进行了综述,介绍了纳观纹理表面往复滑动接触磨损问题试验研究相关成果,探讨了影响摩擦磨损性能的表面纹理参数及其他相关因素,分析了试验研究可能存在的问题。阐述了分子动力学模拟研究该问题的发展现状,介绍了多尺度方法的发展历程,并给出了多尺度方法模拟该问题的算例。最后,探讨了该问题未来可能的发展方向。     

Molecular dynamics simulations of atomic-scale friction in diamond-silver sliding system

Molecular dynamics simulations have been performed to explore the atomic-scale sliding friction, especially the stick-slip friction, in a system consisting of a diamond slider and a silver substrate. The mechanisms of the stick-slip behavior are investigated by considering sliding speeds between 10 m/s and 200 m/s.The analyses of the shear distance between the upmost layer and the downmost layer and displacements of a column of atoms in the slider show that shearing deformation of the slider is the main cause of the stick-slip phenomenon. Our simulations also present that a commensurate fit between the two contact surfaces is unimportant for the stick-slip friction.     

油溶性有机钼添加剂的研究——二仲辛基二硫代磷酸钼性能的评定

本文研究了不同浓度的二仲辛基二硫代磷酸钼加入150~#中性油和10~#汽油机油中的基本性能。对其进行了抗摩、减磨及抗氧化试验。试验表明,油溶性二仲辛基二硫代磷酸钼作为滑润油添加剂,能够有效地降低滑动表面的摩擦和磨损,提高承载能力。特别是低浓度二仲辛基二硫代磷酸钼,直接加入全配方的10~# 汽油机油中,可以得到更好的减摩效果。     

低温下聚合物电介质中的空间电荷及其对介电性能的影响

聚合物电介质材料在低温(接近或低于液氮沸点)下比室温下能俘获更多由电极注入的带电粒子并形成空间电菏,将影响聚合物电介质在低温下的介电性能.本文用电声脉冲法和热刺激电流法(TSC)测量了空间电荷的分布及陷阱能级,表明该现象与聚合物电介质中存在的浅能级局部态有关.本文的研究为选用低温电气绝缘聚合物材料提供了新的依椐.     

平面闸门行走支承滑动摩擦系数计算方法

为了解决平面闸门行走支承滑动摩擦系数计算方法问题,提出了基于黏着理论的滑动摩擦系数计算方法,并将滑动摩擦问题转化成接触面之间的犁沟效应和黏着效应.其中硬材料表面粗糙峰被简化为圆锥体,顶峰的高度在均值附近呈现正态随机分布,应用此随机平面模型对软硬材料之间的犁沟效应进行分析.另外采用"鹅卵石"模型计算黏着效应.此公式在计算摩擦系数与相对滑动速度之间的变化关系时与前苏联学者Крагепьский等提出的变化趋势非常相似,此外其结果还与丁华东等所做的试验结果近似.另外钢对钢、钢对青铜以及钢基铜塑复合材料对不锈钢的摩擦系数随着速度变化的数值与《水利水电工程钢闸门设计规范》(SL74—95)中规定的摩擦系数变化范围很接近.因此证明所提出的公式在计算行走支承滑动摩擦系数时具有一定的可靠性.     

机动飞行中转子轴承系统新型碰摩的动力学行为

采用考虑转静间隙变化和叶片数的新型碰摩模型,同时考虑转子在机动飞行条件下引起的机动载荷和滚动轴承非线性赫兹接触力,建立了转子-滚动轴承-碰摩耦合系统非线性动力学微分方程.利用数值方法分析了转速和机动载荷对系统动力学行为的影响.研究结果表明:机动飞行条件下碰摩转子系统亚谐波共振幅值增加;低速时,碰摩主要激发高频振动,高速时则激发低频振动;机动载荷增加使转子系统振动增大,从而引起转子与定子间的碰摩.     

Observation of shear-induced nematic-isotropic transition in side-chain liquid crystal polymers

Flow-induced phase transitions are a fundamental (but poorly understood) property of non-equilibrium systems, and are also of practical importance for tuning the processing conditions for plastics, petroleum products, and other related materials. Recognition that polymers may exhibit liquid crystal properties has led to the discovery of the first tailored side-chain liquid crystal polymers (SCLCPs), which are formed by inserting a spacer between the main polymer chain and the lateral mesogen liquid-crystalline graftings. Subsequent research has sought to understand the nature of the coupling between the main polymer chain and the mesogens, with a view to obtaining better control of the properties of these tailored structures. We show here that the parallel or perpendicular orientation of the mesogens with respect to the main chain can be reversed by the application of an external field produced by a shear flow, demonstrating the existence of an isotropic nematic phase transition in SCLCPs. Such a transition, which was theoretically predicted for low-molecular-weight liquid crystals but never observed, is shown to be a general property of SCLCPs too. We expect that these SCLCPs will prove to be good candidate systems for the experimental study of these non-equilibrium phenomena.     

滑动摩擦和啮合相位对齿轮中心双流传动动力学的影响

为了研究滑动摩擦和相位调谐对齿轮中心双流传动动力学的影响,建立了考虑时变啮合刚度、阻尼、滑动摩擦、相位及支承刚度和阻尼的齿轮中心双流传动系统扭转－横向振动耦合模型。通过对渐开线直齿轮副啮合过程的分析,推导了系统中与摩擦有关的计算公式,并采用数值仿真法研究了滑动摩擦、相位调谐对齿轮动态传动误差和支承动载荷的影响,研究结果表明滑动摩擦对齿轮支承动载荷影响很大,采用相位调谐可有效地降低系统动态传动误差及中心轮的支承动载荷。     

表面引发ARGET ATRP制备聚合物刷研究进展

综述了表面引发ARGET ATRP制备聚合物刷的最新研究进展,主要包括对无机物基质(SiO2和碳纳米管)和有机物基质(纤维素和聚合物微球)的表面改性。该法不仅催化剂用量少、操作简单,而且聚合可控性好、聚合物接枝密度高、分子质量大,是对材料表面进行改性的有效方法。