基于超平表面的原子力显微镜探针磨损研究

探针磨损是影响原子力显微镜图像质量的关键因素之一。为了研究原子力显微镜(AFM)探针针尖磨损问题,选取超平表面(R_q0.5 nm)作为测试样品,采用材料表面的粗糙度(R_q)评估探针针尖磨损效率。在较低的探针悬臂目标振幅比例(10%),较低反馈回路设定值比例(10%),较低扫描速度(1.0 Hz)以及适中I-gain(1.7)的测试条件下,探针的磨损最小,可以有效地延长探针的使用寿命。最后利用扫描电镜对比了不同测试条件下探针针尖的形貌,推测了探针针尖在连续测试中磨损与断裂的机理。     

Mechanochemistry Induced Using Force Exerted by a Functionalized Microscope Tip

Atomic‐scale mechanochemistry is realized from force exerted by a C₆₀‐functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage‐metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density‐functional calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process cannot be achieved by electrical means.     

Direct Measurement of the Depletion Force Using an Atomic Force Microscope

The interactions between colloidal particles immersed in solutions of a nonadsorbing polymer are of interest in a variety of applications such as paint and ink formulations and mineral processing. In this Letter we report the use of an atomic force microscope to study the interaction forces between a silica particle (of radius 3.8 μm) and a planar silica surface, both bearing a terminally grafted n-octadecyl alcohol sheath (SiO₂-C₁₈), mediated by cyclohexane solutions of poly(dimethyl siloxane) (PDMS). The experimental results are consistent with theories of the depletion interaction between hard, chemically inert surfaces in the presence of free (nonadsorbing) polymer in solution. The length of the measured (attractive) interaction was commensurate with the radius of gyration of the PDMS sample used, and the magnitude of the force increased with increasing polymer concentration. As the surfaces closely approached each other, a short-range steric interaction was observed as the opposing octadecyl chains came into contact, and this interaction was independent of the free polymer concentration.     

Structure and Dynamics of Adsorbed Dopamine on Solvated Carbon Nanotubes and in a CNT Groove

Advanced carbon microelectrodes, including many carbon-nanotube (CNT)-based electrodes, are being developed for the in vivo detection of neurotransmitters such as dopamine (DA). Our prior simulations of DA and dopamine-o-quinone (DOQ) on pristine, flat graphene showed rapid surface diffusion for all adsorbed species, but it is not known how CNT surfaces affect dopamine adsorption and surface diffusivity. In this work, we use molecular dynamics simulations to investigate the adsorbed structures and surface diffusion dynamics of DA and DOQ on CNTs of varying curvature and helicity. In addition, we study DA dynamics in a groove between two aligned CNTs to model the spatial constraints at the junctions within CNT assemblies. We find that the adsorbate diffusion on a solvated CNT surface depends upon curvature. However, this effect cannot be attributed to changes in the surface energy roughness because the lateral distributions of the molecular adsorbates are similar across curvatures, diffusivities on zigzag and armchair CNTs are indistinguishable, and the curvature dependence disappears in the absence of solvent. Instead, adsorbate diffusivities correlate with the vertical placement of the adsorbate’s moieties, its tilt angle, its orientation along the CNT axis, and the number of waters in its first hydration shell, all of which will influence its effective hydrodynamic radius. Finally, DA diffuses into and remains in the groove between a pair of aligned and solvated CNTs, enhancing diffusivity along the CNT axis. These first studies of surface diffusion on a CNT electrode surface are important for understanding the changes in diffusion dynamics of dopamine on nanostructured carbon electrode surfaces.     

原子力显微镜对细胞色素C分子结构的形态研究

用原子力显微镜(AFM)对不同浓度下细胞色素C的分子形态,以及加入蛋白质降聚和变性剂脲后的形态变化进行了考察。实验结果显示,在50μmol/L的低浓度溶液中细胞色素C分子主要以直径为3nm的类球形单体形式存在。浓度增大,细胞色素C分子发生聚集,且随着浓度的进一步增大,细胞色素C分子倾向于形成更大的聚集体。浓度为200μmol/L时,聚集体分子间相互缠绕,形成链状结构。浓度低于0.8mol/L的脲的加入基本不影响细胞色素C分子的形态。加入较高浓度的脲,细胞色素C聚集体的聚集数降低,聚集体分子间没有明显的链状结构。     

Direct Measurement of Repulsive van der Waals Interactions Using an Atomic Force Microscope

The forces of interaction between a flat poly(tetrafluoroethylene) (PTFE) surface and gold spheres (of radii 3–8 μm) were measured as a function of apparent surface separation for different intervening media. For air, fluorinated alkanes, and polar liquids the interaction between the surfaces was found to be attractive. With intervening liquids of low-polarity the interaction was found to be repulsive. This repulsion is attributed to a negative composite Hamaker coefficient leading to van der Waals repulsion.     

Direct Quantification of Aspergillus niger Spore Adhesion in Liquid Using an Atomic Force Microscope

An atomic force microscope has been used to quantify directly the adhesion between single Aspergillus niger spores and freshly cleaved mica surfaces. The measurements used "spore probes" constructed by immobilizing a single spore at the apex of a tipless AFM cantilever. Adhesion was quantified from force-distance data for the retraction of the spore from the surface. Studies in NaCl solutions over a range of pH and electrolyte concentration showed that the decrease of long-range electrostatic repulsion with decreasing pH provided a contribution in increasing the overall adhesion, but the variation of such repulsion with ionic strength did not correlate with changes in the magnitude of adhesion. Specific interactions between appendages and protusions on the spore surface must play an important role in adhesion. The AFM spore probe technique provides a useful new method for evaluating the interactions of spores and surfaces. It has the potential to become a powerful asset for both fundamental studies and the assessment of new materials with low adhesion properties. Copyright 2000 Academic Press.     

甘草多糖螺旋结构的原子力显微镜研究

用原子力显微镜(AFM)对甘草多糖的微观结构进行观察, 实验结果表明, 甘草多糖主要由葡萄糖、阿拉伯糖和半乳糖组成. 甘草多糖分子的稀溶液铺展在Ni^2＋处理的云母片上, 经干燥, 乙醇固定后, 获得稳定、重复的图像. 甘草多糖分子具有高度分枝的结构, 并且糖链间形成环状、柱状或近似于螺旋状的结构. 甘草多糖链呈多股紧密的螺旋结构, 这种现象可能与该多糖中分子间的Van der Waals相互作用以及糖链间氢键缔合有关.     

皂苷、皂苷元分子聚集相行为的原子力显微镜研究

用原子力显微镜检测了不同浓度下皂苷和皂苷元的分子聚集相行为.实验表明,当浓度为1.0×10-5 mol/L时,皂苷形成分散较均匀的小片段结构,表现为皂苷分子的聚集体结构;而皂苷元由多个分子连接形成聚集体结构,与皂苷相比高度起伏较低,链的长度较长.浓度为1.0×10-4 mol/L时,皂苷出现了不规则片层与小片段共存结构;皂苷元却形成多孔的网状结构.当浓度增大到1.0×10-3 mol/L时,皂苷小分子紧密聚集、分布在云母表面;皂苷元则形成紧密聚集的大片层多孔结构.结构分析表明,分子官能团的属性对于皂苷和皂苷元分子形成的不同结构起到了关键作用,分子骨架中的糖链阻碍皂苷形成大片层结构,而皂苷元由于分子骨架中羟基间氢键相连接,易于形成大的片层结构.     

Metal-to-Oxide Charge Transfer Observed by a Kelvin Probe Force Microscope

The charge transfer from a nanometer-sized transition metal particle to a catalyst support is thought to affect reactions over the metal surface. We propose the application of Kelvin probe force microscope, which is an extension of the atomic force microscope, to observe the charge transfer particle-by-particle. Our recent results on Na adatoms, Cl adatoms, Pt adatoms and particles, and Ni particles evaporated on TiO₂(110) are reviewed.     

脂双层膜表面结构与稳定性的原子力显微镜研究

用原子力显微镜研究了1,2－二油酸甘油－3－磷酸－1甘油（DOPG）脂双层膜 的表面结构与稳定性。实验结果表明,原子力显微镜的探针与脂双层膜的相互作用 导致脂双层膜表面产生一个永久的损伤。静电相互作用对脂双层膜结构和稳定性的 影响表明,在NaCl溶液中制成的脂质体,随着NaCl浓度的增加,它们的双层膜更稳 定。在低的NaCl浓度则经常被损伤,在1 mol/L NaCl溶液中制备的指双层变得更稳 定。在KCl溶液中结果恰好相反。在高的KCl浓度中经常被损伤,随着KCl浓度的降 低,它们的双层膜更稳定。葡萄糖和蔗糖对脂双层膜结构有稳定作用。     

原子力显微镜在聚烯烃研究中的应用

聚烯烃材料因其卓越的性能和较低的价格广泛应用于工农业、医疗卫生、军事、日常生活等领域。为了拓展聚烯烃材料的应用范围,表面功能化聚烯烃、聚烯烃与其他材料的共混物以及聚烯烃/无机纳米复合材料等得到了发展,并成为该领域的研究热点。原子力显微镜(AFM)是利用一个极为尖锐的针尖与样品间的相互作用力进行材料表面的形貌、物理和化学信息探测的一种技术,它在上述聚烯烃研究中发挥着重要作用。表面粗糙度是聚烯烃材料表面功能化研究中的重要参数之一,AFM技术则能够给出准确的表面粗糙度信息。由于AFM技术能够直观地观察各组分的混合状态及相分离情况,因此AFM技术成为聚烯烃与其他材料共混研究的重要手段之一。此外,AFM是一种非常有效的微纳米结构形貌的表征方法,在聚烯烃的结晶研究方面也得到了应用。本文简单介绍了AFM表面形貌观测的工作原理和工作模式,主要阐述AFM在聚烯烃材料研究中的三个主要应用:材料表面粗糙度、共混相分离以及结晶研究。     

Motion of a Colloidal Sphere Covered by a Layer of Adsorbed Polymers Normal to a Plane Surface

A combined analytical–numerical study is presented for the slow motion of a spherical particle coated with a layer of adsorbed polymers perpendicular to an infinite plane, which can be either a solid wall or a free surface. The Reynolds number is assumed to be vanishingly small, and the thickness of the surface polymer layer is assumed to be much smaller than the particle radius and the spacing between the particle and the plane boundary. A method of matched asymptotic expansions in a small parameter λ incorporated with a boundary collocation technique is used to solve the creeping flow equations inside and outside the adsorbed polymer layer, where λ is the ratio of the characteristic thickness of the polymer layer to the particle radius. The results for the hydrodynamic force exerted on the particle in a resistance problem and for the particle velocity in a mobility problem are expressed in terms of the effective hydrodynamic thickness (L) of the polymer layer, which is accurate to O(λ²). The O(λ) term forLnormalized by its value in the absence of the plane boundary is found to be independent of the polymer segment distribution and the volume fraction of the segments. The O(λ²) term forL, however, is a sensitive function of the polymer segment distribution and the volume fraction of the segments. In general, the boundary effects on the motion of a polymer-coated particle can be quite significant.     

Emulsification and Foaming Properties of Hydrophobically Modified Gelatin

Surface active gelatins were formed by covalent attachment of hydrophobic groups to gelatin molecules by reactingN-hydroxysuccinimide esters of various fatty acids (C₄–C₁₆) with the lysine groups. The surface activity was evaluated by emulsification and foaming properties, and by adsorption at the oil–water interface. It was found that, in general, the modified gelatins are more surface active than the native gelatin. The increase in hydrophobic chain length and the number of attached alkyl chains per gelatin molecule leads to a decrease in the emulsion droplet's size and to more stable emulsions. Adsorption isotherms, at the o/w interface, show much higher surface concentration, at saturation, of the modified gelatin than the native gelatin. The modified gelatins also have high foaming ability and a high foam stability, while the maximal foam activity is obtained by the C₈modified gelatin. The foaming properties of the surface-active gelatins were also compared to that of sodium dodecyl sulfate (SDS) and it was found that below the CMC of SDS, both foam activity and stability were higher for the modified gelatins. On the other hand, above the CMC the foam activity of SDS was higher, but the foam stability was lower than for C₈–C₁₆-modified gelatins.     

AFM研究蝙蝠葛碱对daudi细胞毒性的影响

利用原子力显微镜、CCK-8实验和流式细胞术研究了蝙蝠葛碱(dauricine)对B细胞淋巴瘤daudi细胞的细胞毒性。蝙蝠葛碱能显著抑制daudi细胞的增殖。CCK-8实验表明,细胞存活率与蝙蝠葛碱浓度存在时间依赖和剂量依赖关系。经10～50μmol/L的蝙蝠葛碱作用24 h后,daudi细胞存活率从(89.8±4.3)%降至(11.2±3.2)%;48 h后,存活率从(68.9±2.6)%降至(2.5±0.5)%。流式细胞术表明蝙蝠葛碱处理dau-di细胞24 h后,凋亡率从5.2%增至28.2%(60μmol/L)。AFM数据显示对照组细胞呈圆形,表面较光滑。经蝙蝠葛碱处理后,daudi细胞坍塌,超微结构显示细胞表面粗糙、凹凸不平。此外,经不同浓度蝙蝠葛碱作用的daudi细胞,其线粒体膜电位随着药物浓度的加大而降低。蝙蝠葛碱能显著抑制daudi细胞生长增殖。     

超高感彩卷乳剂微晶体电镜研究

应用物理和化学相结合的方法，将超高感彩卷分层剥离，离心沉降，水洗除胶，电镜观测各层乳剂的微晶体结构。揭示了超高感彩卷各乳剂层的结构情况，披露了超高感彩剂制造技术。     

Gas-Phase Synthesis of Reactive Molecules Using Adsorbed Reagents

Base-induced elimination reactions have found wide application in the synthesis of strained alkenes. The method is often complicated by a competing process in which the incipient alkene is trapped by nucleophilic addition of the base. Recent studies have shown that the bi-molecular side reactions can be avoided when bases such as potassium tert-but-oxide are supported on an inert surface like silica gel and the reaction is carried out in vacuo. This vacuum gas-solid reaction (VGSR) procedure has the additional advantage that very unstable species may be isolated under conditions that allow detailed studies of their physical and chemical properties. The scope of this procedure has been extended to include the use of fluoride salts supported on glass helices to effect the elimination of β-halosilanes. The fluoride route to strained alkenes is particularly attractive since the reaction may be carried out at very moderate temperatures and the starting materials are readily available. This review describes the development of this vacuum gas-phase procedure and its application in the synthesis and characterization of small-ring alkenes and bicycloalkenes, including methylene-cyclopropene, spiropentadiene, bicyclo-propenyls, 1,2- and 1,3-bridged cyclo-propenes, and other simple cyclo-propenes.     

粘度法测量高分子在玻璃表面上的吸附层厚度

高分子在固体表面上的吸附层厚度对了解其结构具有重要意义．厚度的测量通常采用椭圆偏振法、流体力学法和沉降法等几种方法来测量［１］．流体力学法始创于５０年代中期Ｏｈｒｎ［２］对极稀高分子溶液粘度异常行为的解释．由于高分子在粘度计的毛细管管壁上的吸附,致使...     

Energy Transfer Between Aromatic Hydrocarbons Dissolved in a C18-Surfactant Layer Adsorbed on Laponite

The energy transfer between pyrene and perylene was studied in a system in which the hydrocarbons were dissolved in the surfactant layer adsorbed on the surface of an organoclay prepared by rapid mixing of Laponite clay and a C18 surfactant. The experimental quenching data gave critical energy transfer radii of 53.3 Å. A theoretical calculation of this radius using the Förster approximation indicated a value of 53 ± 7 Å for this interaction. All these values were in good agreement with similar experiments for the energy transfer between the hydrocarbons in organic solvents. Furthermore, the ratio I ₁/I ₃ of the intensities of the vibronic fine structure of the emission spectrum of pyrene in this system was found to be 1.25, similar to the value found for the same probe in several surfactants, indicating that pyrene is localized in the organic layer.