Micro contact and stick-slip number between AFM probe tip and sample surface

Atomic force microscope (AFM) has become a main instrument in characterization of micro topography and micro tribology of surfaces. Under its contact mode, AFM probe tip slides on the surface in the direction perpendicular to its longitudinal axis to get topography and lateral force images simultaneously. During the scanning, the AFM tip is loaded by both a normal force and a lateral force, which make the probe bend and twist. In their pioneering work, Mate et al.[1] used AFM to measure m…     

Adhesion forces for water/oil droplet and bubble on coking coal surfaces with different roughness

Surface roughness plays a significant role in floatability of coal. In the present paper, coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements. The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness. The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning. Maximum adhesion forces between water and surfaces were 111.70, 125.48, and 136.42 μN when the roughness was 0.23, 0.98, and 2.79 μm, respectively. In contrast, under a liquid environment, the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water. Maximum adhesion forces of increasing roughness were 97.14, 42.76, and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48, 145.84, and 121.02 μN between oil droplet and surfaces, respectively. Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.     

Effect of roughness on wettability and floatability: Based on wetting film drainage between bubbles and solid surfaces

Wetting film thinning measurement was introduced to clarify the wettability and floatability of solid surfaces with varying roughness. The wettability was quantified using the contact angle measurement combined with the dynamic force microbalance test between solid surfaces and water droplets, while the floatability was investigated by the bubble-solid surface dynamic attachment observation and the induction time measurement. The results show that the water contact angles reduce (14.53°, 12.74°, and 6.71°) with the increase of glass surface roughness, while the water droplet-glass adhesion forces intensify (11.1, 19.1 and 19.2 μN) owing to the stable wetting film. The distortion of the contact surface and the Wenzel state are the causes. In contrast, the hydrophobized surfaces have the growing apparent contact angles (38.08°, 69.81°, and 81.01°), declining adhesion strength and shortening induction time (863, 352 and 12 ms) along with the increasing surface roughness. The weak wettability and fine floatability on the rough hydrophobized surface is reflected in the fast wetting film drainage dynamics and three-phase contact formation, which may be attributed to the wetting film with short diameter on tiny rough nubs and the entrapped air in the grooves as a bridge between the bulk bubble and the solid surface.     

轻敲模式下原子力显微镜的能量耗散机理研究

为研究原子力显微镜(AFM)在轻敲工作模式下的能量耗散机理,基于Hamaker假设和Lennard-Jones势能定律得到了原子与球体间的作用力．通过将球体与平面原子间的作用力等效为球体与平面间的粘着分布力,并结合经典弹性理论建立了一种新型的球体与平面粘着接触的弹性模型,根据所建模型得到了AFM针尖与样品表面间的粘着力随其间距的变化规律．仿真结果表明,粘着力随间距的变化曲线在AFM针尖趋近和撤离样品表面,即加载和卸载的两个过程中并不完全相同,产生了粘着滞后现象,而粘着滞后现象的出现表明AFM在轻敲工作模式中将耗散能量,因而,所建模型从理论上证实了AFM在轻敲工作模式下存在能量耗散现象．     

上浆剂使用浓度对碳纤维性能的影响研究

为了改善碳纤维表观性能及其复合材料界面性能,不同浓度的上浆剂用于碳纤维表面上浆．采用原子力显微镜（AFM）、动态接触角测试仪（DCAT）和微复合材料界面结合强度（IFSS）等研究了上浆剂浓度对碳纤维的表面形貌,表面能及对微复合材料界面性能和耐湿热老化性能的影响．实验结果表明：上浆剂的使用浓度对碳纤维表观性能影响较大．A...     

原子力显微镜"突跳"研究

“突跳”现象严重影响着原子力显微镜(AFM)的性能．根据Hamaker微观连续介质理论,建立了AFM针尖同试样面接触力包含斥力的数学模型;分析了AFM悬臂梁弹性力同针尖接触力的关系,发现了引起AFM“突跳”的本质是弹性力同接触力的不稳定平衡问题;通过增加AFM悬臂梁刚度,提出了一种避免“突跳”现象发生的方法,并给出了仿真结果。     

Molecular Dynamics Simulation on Friction and Thermal Propertiesof FCC Copper in Nanoscale Sliding Contacts

面心立方单晶铜纳观滑动接触摩擦性能与热特性的分子动力学研究

佟瑞庭¹,韩宾²,张涛³,权泽芬⁴,刘更¹

(1. 西北工业大学 陕西省机电传动与控制工程实验室,西安 710072;

2.江苏自动化研究所,江苏 连云港 222061;

3.中国运载火箭技术研究院,北京 100076;

4.上海飞机设计研究院,上海 200232)

摘要：

在纳观滑动接触过程中,粘着效应和粘着力占主导地位,导致滑动接触表现出很高的摩擦力。绝大部分的摩擦功转化为摩擦热,而摩擦热会使纳米材料变软,并进一步影响摩擦行为,因此研究纳观滑动接触的摩擦性能与热特性具有重要意义。本文建立一个刚性圆柱压头与一个弹性基体纳观滑动接触问题的分子动力学模型。研究了不同滑动速度和不同压头半径情况下,基体的热特性以及摩擦行为。结果表明：在低速滑动时,摩擦力的波动主要是材料的熔化-凝固造成的,而在高速滑动时,材料的熔化是摩擦力降低的主要原因。随着滑动速度的增大,平均摩擦力先升高后降低,而基体的平均温度随滑动速度的增大而升高。增大压头的半径使基体温度有很大的提升,但压头半径对摩擦力的提升效应与高温对摩擦力的降低作用相互耦合,使得摩擦力仅呈现出较小程度的提高。

关键词：分子动力学;摩擦性能;热特性;纳观滑动接触

     

Effect of crack face contact on dynamic stress intensity factors for a hole-edge crack

In order to determine the dynamic stress intensity factors(DSIFs)for a single edge crack at the center hole of a finite plate under a compressive step loading parallel to the crack,the finite element method was employed to solve the cracked plate problem.The square-root stress singularity around the crack tip was simulated by quarter point singular elements collapsed by 8-node two-dimensional isoparametric elements.The DSIFs with and without considering crack face contact situations were evaluated by using the displacement correlation technique,and the influence of contact interaction between crack surfaces on DSIFs was investigated.The numerical results show that if the contact interaction between crack surfaces is ignored,the negative mode I DSIFs may be obtained and a physically impossible interpenetration or overlap of the crack surfaces will occur.Thus the crack face contact has a significant influence on the mode I DSIFs.     

有机复合客土基材接触面剪切力学特性试验

为研究高分子材料和接触面粗糙度对土-岩接触面剪切力学性能的影响，设计预制混凝土模块作为岩面相似材料，开展一系列改进型直剪试验，分析高分子材料和接触面粗糙度的影响规律，并结合扫描电镜试验深入揭示高分子材料的改良机制。结果表明，高分子材料主要通过提高黏聚力极大地改善基材土和接触面的剪切力学性能，掺量2%的基材试样黏聚力达41.76 kPa,提高了约3倍。掺量2%的不同接触面试样黏聚力提高了2～7倍；增大接触面粗糙度主要通过提高黏聚力增强接触面剪切力学性能，粗糙度为6.5 mm的不同接触面间黏聚力提升幅度为12.27～23.77 kPa,提高了0.4～3.9倍；对于平坦接触面和粗糙接触面，高分子材料对剪切性能的强化表现为两种不同模式；高分子材料与接触面粗糙度对接触面的剪切性能具有协同强化效应。     

外加电场对云母表面纳尺度摩擦行为的影响

利用原子力显微镜（AFM）研究了施加恒定外电场时,AFM针尖与云母表面间的摩擦力变化情况．结果表明,对样品基底施加一定偏压后,由于针尖与云母表面间的静电作用增强,使得针尖与样品间的总相互作用势增加,从而导致针尖与云母间的摩擦力比未施加偏压时大,且摩擦力大小随电压升高而增大．尤其是施加负偏压时,摩擦力增加更为显著,且大于正偏压时的摩擦力．     

石英表面阳离子吸附膜结构的AFM研究

为了研究阳离子表面活性剂对固体表面的润湿性的影响,了解表面活性剂在石英表面的吸附机制,利用原子力显微镜(AFM)技术,考察了不同结构阳离子改性石英片与不同基团改性AFM探针间的拉脱力,从分子角度探索石英表面双层膜的结构特性.研究发现:直链烷基季铵盐CI6PC改性石英片与阴离子改性探针间的拉脱力随浓度增大在临界胶束浓度附...     

辐射空调房间表面的角系数

辐射空调房间内围护结构表面之间的角系数,以及人体表面与室内维护结构表面之间的角系数,是计算室内辐射热交换的基本参数。目前,有关人体、辐射板、门、窗等表面和其它围护结构表面间的角系数通常较难求解,这里避开了采用传统的直接积分法求解角系数,而是利用对表面边界曲线的角系数积分公式,推导出了相互垂直以及相互平行情况下两矩形表面间的角系数表达式,其过程较为简单;同时把人体形状适当地简化为1个六面体固体,得到了人体与维护结构表面之间的角系数。所得结论不受围护结构表面大小及相对位置的限制,可以有效地求解与人体、辐射板、门、窗等表面相关的角系数。     

硝胺填料和高分子键合剂的表(界)面特性表征

对高分子键合剂和硝胺填料的表（界）面特性进行了研究应用Ｋａｅｂｌｅ公式计算了高分子键合剂和硝胺填料的表面能和粘附功，考察了高分子键合剂的羟值与表面能极性分量的对应关系。对溶胀比、初始模量等关系的讨论，阐明了高分子键合剂可在硝胺填料周围形成高度交联的高分子壳层，并产生界面增强效应由ＴａｐｐｉｎｇＭｏｄｅＡＦＭ获得的纳米级表面形貌图像，发现加入丙烯酸甲酯单体，高分子键合剂可形成网络结构     

Investigation of atomic structure ahead of crack tip by STM and AFM

Ｔｈｅｄｉｓｌｏｃａｔｉｏｎｅｍｉｓｓｉｏｎｆｒｏｍｔｈｅｃｒａｃｋｔｉｐａｎｄｔｈｅｎｕｃｌｅａｔｉｏｎａｎｄｐｒｏｐａｇａｔｉｏｎｏｆｍｉｃｒｏｃｒａｃｋｓｃａｎｂｅｓｔｕｄｉｅｄｂｙｉｎｓｉｔｕｔｅｎｓｉｌｅｔｅｓｔｕｎｄｅｒａｔｒａｎｓｍｉｓｓｉｏｎｅｌｅｃｔｒｏｎｍｉｃｒｏｓｃｏｐｅ(ＴＥＭ)[1—3].Ｈｏｗｅｖｅｒ,ｔｈｅｒｅｉｓｎｏｓｔｕｄｙｏｎａｔｏｍｉｃｓｃａｌｅｍｉｃｒｏｓｔｒｕｃｔｕｒｅｏｆｃｒａｃｋｔｉｐｓ,ｅｓｐｅｃｉａｌｌｙｏｎｔｈｏｓｅｏｆｌｏａｄｅｄｃｒａｃｋｓ.Ｆｏｒａ…     

扩展的Langmuir法在低电位平板型颗粒相互作用中的应用

带电颗粒双电层之间相互作用力和能的表达式在很多工业过程的模拟和优化等方面有着广泛的应用。给出了两个平行平板颗粒处在恒电位条件时,相互作用力和相互作用能的简单计算方法。虽然这是对Poisson-Boltzmann方程在高电位情况下进行非线性简化的一个结果,然而由于它和低电位时的电位变化特点是相似的,所以适用于低电位条件下相互作用力和相互作用能的计算。由于保持了Poisson-Boltzmann方程非线性的原型,所以当颗粒之间的距离小的时候,它对高、低电位的等同平行平板型颗粒都是适用的,和精确的计算机数值解的比较表明,它的近似程度是令人满意的。     

原子力显微镜在ZAO薄膜表征中的应用

利用磁控溅射法在溅射功率分别为30,50,80,100W条件下制备ZAO薄膜,并通过原子力显微镜(AFM)、X射线衍射(XRD)谱对制得的薄膜样品进行表面形貌、结构特性和黏附性能进行研究。XRD结果表明,随着溅射功率的增加,ZAO薄膜呈现了明显的(002)择优取向,结晶质量获得提高。通过原子力显微镜对样品的二维、三维以及剖面线图进行分析。随着溅射功率增大,薄膜样品表面较均匀致密,晶粒生长较充分,结晶质量较高,粗糙度和黏附力均增大。     

基于浸润参数和表面能理论的沥青与集料黏附性分析

为了解决沥青与集料黏附性缺乏量化评价方法的问题,分别采用光学接触角测量仪、表面张力测试仪和自动压汞仪对沥青与集料的接触角、沥青表面张力和集料的孔隙分别进行了测定,通过试验结果对沥青与集料的浸润参数和表面能参数进行了计算,并据此对沥青与集料的黏附性进行了评价;分析了沥青与集料黏附性的影响因素,并通过测定不同温度下沥青的表面张力,结合理论分析建立了沥青表面张力与温度的关系模型.研究结果表明:可以采用浸润参数和表面能理论对沥青与集料的黏附予以评价;较大的孔隙度和平均孔径有利于集料对沥青的吸附;沥青对集料的浸润深度h越大、浸润时间t越短,有利于产生更好的浸润效果;沥青与集料黏附功和浸润功越大,浸润性越好;沥青与集料间的黏附性与沥青表面张力、沥青与集料接触角以及集料表面特性等因素有关.     

乙酸酐改性氨基聚硅氧烷的成膜性及膜形貌研究

应用原子力显微镜（AFM）和接触角测量仪对乙酸酐改性氨基聚硅氧烷的成膜性及膜形态进行了研究。结果发现，氨基聚硅氧烷在单晶硅基底上均能成膜，但不同的氨基聚硅氧烷所形成的膜形貌不同，膜的表面形貌实际上与基团的排列方式有关，氨乙基氨丙基聚二甲基硅氧烷在单晶硅基底上可形成均匀、平薹、光滑的疏水膜，而乙酸酐改性的氨乙基氨丙基聚二甲基硅氧烷则形成凹凸不平、粗糙的具有弱亲水性的非均匀膜。     

Theoretical and experimental study of 2D conformability of stretchable electronics laminated onto skin

Smoothly attaching the stretchable epidermal electronic devices(EEDs) onto the skin surface is highly desired to improve the measurement accuracy of electrophysiological signal.The paper presents an analytical approach to study interfacial mechanics of the 2D planar EEDs on the checkerboard buckling patterns of human skin.Energy variation method is proposed to determine a criterion whether EEDs laminate conformally onto the skin surface under undeformed and stretched cases.EEDs with low bending stiffness(thin,soft devices/backing layer),smooth and soft skin,and strong adhesion promote conformal contact.Furthermore,the adhesion energy at the EED/skin interface is measured by the homemade peeling experiment platform with different substrate thicknesses and areal coverages.The upper limit of the areal coverage for EED conformal contact with the skin is proposed with given EED/skin properties.Conformability of EEDs are validated by experiments with different substrate thickness,areal coverage and external loadings.It provides a design guideline for EED to conformally contact with the skin surface for more accurate biological signal monitoring.     

碳离子注入对硅片表面黏附性能的影响

为了改善单晶硅材料表面的黏附性能,对单晶硅片进行碳离子注入,注入剂量为2×10~(16)ions/cm~2,注入能量分别为40 keV和80 keV.采用X射线衍射、X光电子能谱仪和三维轮廓仪研究了碳离子注入前后硅片的晶体结构、化学组分及其面粗糙度,通过接触角测定仪和扫描探针显微镜测量了碳离子注入前后硅片表面的接触角和黏附力的大小.结果表明:碳离子注入改变了硅片表面的晶体结构,在表面形成富含碳和碳化硅的改性层,较注入前粗糙度和接触角分别增加70%～90%和1.7～1.8倍;随着碳离子注入能量的增大,疏水性的碳和碳化硅增多,粗糙度和接触角分别增加9.5%和3.4%.在33%和70%这2种相对湿度条件下,碳离子注入后硅片表面的黏附力分别减少54%～57%和34%～37.3%;碳离子注入能量增加,黏附力分别减小6.7%和4.8%.相对湿度从33%增加到70%时,单晶硅、注入能量为40 keV和80 keV的硅片表面的黏附力分别增加1.24,2.22,2.28倍.