官能团对自组装分子膜摩擦特性的影响

在原子力显微镜上,对分子链长相同、官能团不同的两种自组装分子膜的摩擦特性进行了研究,分析了载荷和滑动速度对自组装分子膜摩擦特性的影响.结果表明:自组装分子末端官能团的化学活性越强,形成的自组装分子膜的团簇特征越显著;对于两种短链自组装分子,摩擦力随着载荷的增大而增大,而滑动速度的影响在自组装分子末端官能团化学活性较大时才表现出来.形成结构稳定的自组装分子膜后,摩擦力比成膜初期的自组装分子膜显著降低,具有减摩效应.具有较强化学活性官能团的自组装分子膜,当载荷增加到一定值以后,会失去减摩效应,其化学活性越强,摩擦力越大.     

基于自组装技术改性处理镁和铝金属的摩擦学特性研究

采用自组装技术对镁、铝金属表面进行改性处理,并对制备的试样进行紫外照射.利用接触角测量仪、原子力显微镜和UMT-2型微摩擦磨损试验机对制备的试样进行表征和摩擦学特性测试,分析了载荷、滑动速度以及紫外照射对试样摩擦学特性的影响.结果表明,经OTS自组装分子膜改性处理的镁、铝金属表面平整均匀,具有疏水特性和良好的摩擦学性能.Si3N4球与OTS自组装分子改性处理试样间的摩擦系数随载荷和滑动速度的增大而增大.紫外照射5min可有效地提高OTS自组装分子膜改性处理的效果,减小了有机杂质的粘着效应.改性处理的镁、铝金属表面在降低摩擦系数的同时,摩擦副的耐久性显著提高.     

OTS自组装分子膜的制备及其摩擦学测试

采用分子自组装技术在银片表面成功制备了十八烷基三氯硅烷单层膜(OTS-SAMs).运用接触角测试仪、极化曲线、循环伏安、SEM和紫外-可见分光光度计(UV-Vis)对OTS-SAMs薄膜的结构、形貌和性能进行了表征,并分析了载荷和滑动速度对薄膜摩擦学特性的影响.结果表明:紫外光照使基板由疏水变为亲水.极化曲线和循环伏安图显示在组装初期180s内,十八烷基三氯硅烷水解产物主要是与基体表面的羟基发生聚合反应,表现为“岛式”结构增长,随着组装时间的增加,有机硅烷分子之间发生聚合,当组装30min后,成膜过程趋于稳定,可以在基体表面形成平整、牢固和致密的自组装薄膜,这一结果同样由SEM得到验证.随着自组装膜的完善,其摩擦力降低,达到润滑的效果.另外,通过实验结果初步分析了OTS-SAMs的形成机理.     

硅氧烷修饰聚芳醚酮自组装薄膜的制备及摩擦性能

将杂萘联苯聚芳醚酮(PPEK)经硼氢化钠还原、环氧基三甲氧基硅烷改性后,合成了侧链含有硅氧烷官能团聚芳醚酮,研究了其在玻璃基底上的自组装行为,并用红外、固体29Si-NMR谱、原子力显微等对薄膜进行了表征。结果表明,聚芳醚酮的自组装过程在室温下1 h内即可完成。与短链分子自组装膜相比,自组装聚芳醚酮膜具有良好的减摩抗磨性能,当载荷为100 mN时自组装薄膜的稳定摩擦系数为0.1左右,且摩擦系数随着滑动速度的增加而减小。     

分子自组装技术基底材料的研究进展

综述了用于分子自组装技术的基底材料的种类及自组装分子膜的制备过程,结合多种表征方法的测试结果介绍了各类自组装分子膜的吸附特性、组装机理、功能特点、应用领域及影响薄膜性能的各种因素,还介绍了在自组装单分子膜表面制备其它无机功能薄膜的研究结果。     

MB8镁合金疏水/超疏水表面制备与微摩擦特性研究

通过微弧氧化技术在MB8镁合金表面形成微细表面结构,再利用自组装方法在微弧氧化层表面制备1H,1H,2H,2H-全氟葵烷基三氯硅烷(FDTS)自组装分子膜。采用扫描电镜、表面粗糙度仪、X射线衍射仪、表面硬度仪、接触角测量仪和UMT-2型摩擦磨损试验机评价膜层形貌结构、力学特性、润湿性及其微摩擦学特性。结果显示,镁合金表面经微弧氧化处理和自组装分子膜修饰后,表面润湿性经历了由亲水到超亲水再到超疏水的转变过程。超疏水表面的获得是由微弧氧化处理得到的表面粗糙结构和低表面能物质自组装分子膜共同作用的结果。对试样进行摩擦磨损测试的结果显示,致密层和疏松层以及经自组装分子膜修饰后的膜层均具有比镁合金基底更好的抗磨性能;基于自组装技术制备的疏水、超疏水表面形成的边界润滑膜在一定载荷条件下均能有效地减少基底的摩擦系数,边界润滑膜失效后,基底表面特性占主导地位。     

微图案BiFeO_3薄膜的光刻自组装制备与表征(英文)

利用光刻自组装技术在玻璃基板上成功制备出图案化的BiFeO3薄膜.AFM和接触角测试表明,紫外光照射引起十八烷基三氯硅烷(OTS)单层膜改性,形成憎水的自组装单分子(SAM)区域和亲水的硅烷醇区域;XRD和XPS结果显示,OTS单层膜和紫外照射处理的玻璃基板表面诱导吸附的薄膜为纯相六方扭曲钙钛矿结构的BiFeO3薄膜;SEM和EDS表明,SAM区域沉积的BiFeO3薄膜不连续,在超声波震荡下容易脱落,而硅烷醇区域沉积的BiFeO3薄膜致密均一,与基底结合牢固,边缘轮廓清晰.     

表面润湿性对水润滑Al-Mg合金摩擦学特性的影响

通过自组装技术在Al-Mg合金表面制备自组装分子膜,采用接触角测量仪测定了自组装分子膜的水接触角,采用多功能摩擦磨损试验机对制备不同自组装分子膜的Al-Mg合金在3种润滑方式下进行摩擦磨损实验。结果表明,制备自组装分子膜可显著改变Al-Mg合金的表面润湿性,制备FDTS、FOTS、OTS自组装分子膜的表面呈疏水性,制备MPS、APS自组装分子膜的表面则呈亲水性,5种自组装分子膜接触角由大到小的顺序为FDTS>FOTS>OTS>MPS>APS。自组装分子膜的疏水性越强,Al-Mg合金的摩擦系数越小。同种自组装分子膜在干摩擦条件下摩擦系数最大,浸水润滑条件下摩擦系数有所下降,喷水润滑条件下摩擦系数最小。     

表面润湿性对水润滑Al-Mg合金摩擦学特性的影响

通过自组装技术在Al-Mg合金表面制备自组装分子膜,采用接触角测量仪测定了自组装分子膜的水接触角,采用多功能摩擦磨损试验机对制备不同自组装分子膜的Al-Mg合金在3种润滑方式下进行摩擦磨损实验。结果表明,制备自组装分子膜可显著改变Al-Mg合金的表面润湿性,制备FDTS、FOTS、OTS自组装分子膜的表面呈疏水性,制备MPS、APS自组装分子膜的表面则呈亲水性,5种自组装分子膜接触角由大到小的顺序为FDTS>FOTS>OTS>MPS>APS。自组装分子膜的疏水性越强,Al-Mg合金的摩擦系数越小。同种自组装分子膜在干摩擦条件下摩擦系数最大,浸水润滑条件下摩擦系数有所下降,喷水润滑条件下摩擦系数最小。     

分子沉积膜的力学特性研究

在金衬底上制备了分子沉积膜。用原子力显微镜研究了它的摩擦力,结果表明沉积膜能明显地减小摩擦力。用纳米压痕仪研究它的纳米力学特性,结果表明在金表面沉积一层膜后,弹性模量、硬度和载荷都减小,说明分子沉积膜能改善金衬底的纳米力学特性。     

润滑状态下线接触滑动粗糙界面的动摩擦特性研究

滑动粗糙界面的摩擦润滑特性对界面的润滑设计和润滑状态预测具有重要的理论和实际意义。本文通过建立不同润滑状态下的滑动粗糙界面模型,基于界面的法向载荷由润滑油膜和粗糙体共同承担的载荷分配思想,采用Greenwood-Williamson统计模型描述粗糙表面形貌,考虑界面润滑的时变效应和润滑油的粘-压特性,建立了线接触滑动粗糙界面的油膜厚度方程和粗糙体接触压力方程,获得了整个润滑区的润滑油膜载荷比例因子、油膜厚度和摩擦系数随滑动速度的变化关系,推导了界面由混合润滑过渡为液压润滑的临界速度关系表达式,分析了滑动粗糙界面的润滑承载机理,获得了界面油膜厚度、摩擦系数和临界速度随界面形貌参数、法向载荷、润滑油属性参数的变化规律,为机械结构的界面润滑设计、润滑状态预测和润滑优化提供理论和实验参考。     

Site-selective assembly of quantum dots on patterned self-assembled monolayers fabricated by laser direct-writing

A simple and efficient route for quantum dot (QDs) patterning using self-assembled monolayers (SAMs) as templates is described. By means of a laser direct-writing (LDW) technique, SAMs of octadecylphosphonic acid formed by adsorption on native oxide layer of titanium film were patterned through laser-induced ablation of the SAM molecules. This technique allows the creation of chemical-specific patterns accompanied by slight change in the topography. Using atomic force microscopy and friction force microscopy, the dependence of feature size and characteristics on the irradiation dose was demonstrated. Upon immersion of a substrate with patterned SAMs bearing thiol as the terminal group into a dispersion of QDs resulted in the assembly of QDs on the specific thiol-terminated areas. Patterns of QDs with different photoluminescent wavelength were generated. The LDW technique, which is convenient and flexible due to its path-directed and maskless fabrication process, provided a new powerful approach for patterning materials on surfaces for various applications.     

国内外自组装膜的研究进展

介绍了国内外自组装膜的一些理论研究及成果,阐述了自组装分子、基底、环境因素(湿度和温度)和滑动速度等因素对自组装膜的摩擦学性能的影响,总结了自组装膜的发展状况,并提出了今后的研究重点。     

Amontonian friction induced by flexible surface features on microstructured silicon

Friction between nonadhering sliding surfaces are normally described by Amontons' law, which states that there exists a linear relationship between the friction force and the normal applied load and that the friction force is independent of the macroscopic contact area between the surfaces and the sliding velocity. In this study we have measured friction as a function of applied load between a spherical silica particle and a microstructured silicon surface consisting of arrays of vertical microneedles, and we have challenged Amontons' law by changing the size of the silica particle and the sliding velocity. First, when looking at the friction as a function of time for a given applied load, the friction force was observed to oscillate with a period related to the spacing between the microneedles when using a small silica particle, whereas the friction force exhibited a more random variation when a larger silica particle was used. The oscillation in the friction force is a direct evidence for bending and release of individual microneedles and the observation illustrates that the energy dissipating mechanism becomes hidden in the friction data when the dimensions of the sliding body becomes much larger than the length scale of the surface features causing the friction. Second, when looking at the average friction force as a function of applied load we find, in accordance with Amontons' law, a linear relationship between the friction force and the applied load and the friction force is independent of both the size of the sliding silica particle and of the sliding velocity. One exception from this, however, was observed when sliding a small silica particle at low velocity, where a deviation from Amontons' law was noticed. The deviation from Amontons' law is suggested to be attributed to a change in the energy dissipating mechanism giving rise to the friction force. In light of that it is suggested that Amontons' law only is valid as long as the main energy dissipating mechanism does not change with the applied load. To get a better understanding of the general validity of Amontons' law, our results were evaluated against different microscopic models.     

平整二钛酸钾薄膜的制备及其气相光催化活性

采用溶胶-凝胶法制备了K2Ti2O5薄膜并进行表征;在K2Ti2O5薄膜表面上形成致密的十八烷基三氯硅烷(C18H37SiCl3,OTS)单层自组装膜(SAMs);用OTS SAMs 水接触角变化研究薄膜的气相光催化活性;测量了薄膜的光电流响应.研究发现:K2Ti2O5薄膜表面平整、均匀、致密、在玻璃基片上透明;在紫外和可见光区都有光吸收;K2Ti2O5薄膜上OTS SAMs在空气中用254nm的紫外光照射时降解速度比在TiO2薄膜上快;K2Ti2O5薄膜产生阳极光电流,比TiO2薄膜具有更强的光激发和更稳定的光电流响应.结果表明,K2Ti2O5薄膜在空气中用紫外光照射能很有效的分解OTS SAMs,是一种很好的治理气相有机污染物的光催化剂.     

射频溅射MoS2,WS固体润滑膜在脂润滑下的摩擦学特性

用球－盘试验机研究了射频溅射ＭｏＳ２，ＷＳ２固体润滑膜在脂润滑下的摩擦学特性，并用ＸＰＳ，ＳＥＭ和ＥＤＸ等方法进行了分析．结果指出，在锂基脂润滑下，表面溅射ＭＯＳ２薄膜后摩擦系数降低，擦伤载荷成几倍或几十倍增长，尤其在高滑动速度下效果更加明显，可在一定载荷范围内代替２＃主轴油进行润滑，摩擦中ＭＯＳ２膜表层组织很容易剥落，摩擦中与基体结合较牢的主要是表面下的有效膜厚。因而在本试验条件下两种厚度ＭＯＳ２膜的摩擦学性能基本无差别，溅射ＷＳ２膜中含氧量很高，且在整个膜层中均以ＷＯ３存在，因此减摩效果不理想。     

Molecular dynamic simulation and characterization of self-assembled monolayer under sliding friction

The frictional mechanisms of a self-assembled monolayer (SAM) during nano-scale sliding are studied using molecular dynamics (MD) simulation. The MD model consists of a gold slider and gold substrate with n-hexadecanethiol SAM chemisorbed to the substrate. The trajectory, tilt angles, normal forces, frictional forces, friction coefficients and potential energies per molecular chain of the SAM molecules are evaluated during the frictional process for various parameters including as sliding height, sliding direction (i.e. pro- or anti- the SAM tilt angle), sliding velocity and system temperature. The various parameters are discussed with regard to frictional forces, mechanisms and SAM structural transition. Results show that stick-slip occurs and is related to the sliding period and tilt angle of the SAM molecules. Amplitude of the stick-slip cycle increases with decreasing sliding height until reaching a critical sliding height, which is characterized such that sliding below the critical height causes irreversible changes in the SAM molecular organization and cumulative loss of SAM lubricating efficiency. Different SAM recovery mechanisms were found for different sliding directions relative to SAM tilt angle (pro- or anti-tilt). In both cases, minimum friction occurred during the SAM tilt-angle recovery phase. The friction force curves for these two cases also showed a regular phase shift above the critical height. For stick-slip sliding above the critical height, anti-tilt sliding had significantly lower average friction, but this trend inverted below the critical height. Sliding lower than the critical height cause progressive disorder of the SAM structure and the characteristic differences between pro- and anti-tilt sliding were progressively lost.     

Wear, friction and sliding speed correlations on Langmuir-Blodgett films observed by atomic force microscopy

The dependence of friction and wear on sliding parameters has been investigated with an atomic force microscope. Measurements have been performed on Langmuir-Blodgett monolayers. For the purpose of this study a special counterion polymer has been used to supply a facile insight into the friction and wear dependence on the scan velocity. With a minimum constant load in the order of 10⁻⁸ N, wear has been observed to occur randomly at film defect sites but also on initially intact film areas. Wear is always accompanied by an increase of friction forces. A wearless friction dependence on the scan velocity could not be observed.

The process of wear is discussed in terms of shear forces and adhesive contact forces. Whereas the plastic deformation at the film defect sites can be explained by shear forces, the wear process on initially defect free surfaces could be related to adhesive forces and quantified.     

Cell adhesion and related phenomena on the surface-modified Au-deposited nerve microelectrode examined by total impedance measurement and cell detachment tests

This study investigated alkanethiolate self-assembled monolayers (SAMs) of varied chain lengths adsorbed upon novel Au-coated microelectrodes, of which the surface properties were quantitatively evaluated by surface characterization and 3T3 fibroblast cell adhesion, total impedance and cell detachment tests. Thin-film SAMs adsorbed upon Au/PI/Si provided a hydrophobic or passive surface with increased water contact angle and initial total impedance. From cell adhesion tests, we can observe that the film formed as a dense-packed spacer resulted in incomplete cell sealing of 3T3 cells upon the surface-modified microelectrode. Thus the decrease in cell coverage rate and in the slope in association with total impedance as a function of cell-surface reaction time can be found. To study the adhesion force of a comparable single cell attached upon varied modified surfaces, a cell detachment test using a triangular probe tip of a well defined cantilever was carried out in medium containing fibroblast cells. Overall, both the peak force and the work required to detach a comparable single cell from the anchoring domain corresponded well to the increased length of alkyl chains adsorbed upon Au/PI/Si. Both measurements on the SAM modified surfaces demonstrated much smaller values than those on the pristine Au/PI/Si surface. These results concluded that a cell-repulsive characteristic was clearly formed on the SAM modified microelectrode surface. The non-adhering properties of surface-modified microelectrodes should provide better sensitivity for neuromuscular stimulation as well as for the recording of infinitesimal neural signals in future applications of neural prostheses.