表面、界面的作用与粘接机理〔二）

介绍了材料粘接过程界面区的酸碱作用与化学反应对粘接性能的贡献，其内容包括氢健力的作用，酸碱配位作用的考查，酸碱作用对粘接性能的影响和界面化学结合的形成途径及其对粘接性能的影响。     

表面、界面的作用与粘接机理(二)

介绍了材料粘接过程界面区的酸碱作用与化学反应对粘接性能的贡献,其内容包括氢键力的作用,酸碱配位作用的考查,酸碱作用对粘接性能的影响和界面化学结合的形成途径及其对粘接性能的影响.     

表面、界面的作用与粘接机理(三)

介绍了粘接体系界面的扩散作用、机械作用、双电层吸引作用以及弱界面层的产生及其对粘合性能的影响,另外。讨论了现代表面分析技术如ESCA、ATR、EPMA、SEM、STM及AFM等在表面、界面表征中的应用简况。     

表面改性剂改进结构件界面粘接性能研究

采用表面改性剂(改性硅烷类偶联剂)对粘接界面进行活化,对金属与复合材料、金属与金属粘接性能受表面改性剂的影响进行了试验和分析。结果表明,经表面处理后,粘接强度有很大的提高,已在某型号飞机典型零件上进行了验证。     

材料的表面能与粘接界面的酸碱作用

综述了作者对材料表面能与粘接界面的酸碱作用的研究简况,主要内容包括：（１） 　聚合物表面能的测算;（２） 　金属与无机非金属材料表面能的测算;（３） 　丙烯酰胺（ 丙烯酸） － 天然橡胶接枝聚合物的酸碱作用;（４） 　界面酸碱作用对聚合物抗凝血性能的影响;（５） 　硅烷偶联剂酸碱作用的研究;（６） 　 Ｅ Ｖ Ａ 泡沫材料粘接界面的酸碱作用等。介绍了各有关的研究方法及主要研究结果。     

聚钛硅氧烷凝胶与铝、铁界面粘接机理

用扫描电镜SEM和X射线能量散布分析EDAX技术研究了聚钛硅氧烷 (PTS)与铝、铁基材界面 ,结果发现了PTS与铝界面有良好的结合 ,该结合机理被认为是铝氧化物与PTS产生化学反应 ,形成互渗层的结果 ,随热处理温度提高互渗层厚度增加 ;与上述结果相反 ,PTS与铁基材界面没有明显的化学结合 ,随热处理温度提高界面缺陷增加     

粘接的界面化学

所谓粘接就是将2个不同的固体，用第3种物质连接在一起的技术。然而，大家都知道，如果使2种物质接近于纳米距离，在色散力、偶极力等引力的作用下，它们也可连接到一起，但是，同一种固体之间，如果仅靠接触是不能连到一起的，压合2个做过镜面抛光的固体，并尽可能地排除中间的空气，这样虽然它们之间也有一点连接力，但只要受到微弱的冲击，就会完全破裂，无论是怎样精细抛光加工过的表面，都不可避免地还要有数个纳米的凹凸，既便使这样的表达接近，也只有其中极少的表面能够接近到引力可作用到的距离。由于表面都有微小的凹凸，既便使其接触，也不可能形成一个完全的接触面，将这样的2个固体之间的空隙，用胶粘剂来充填，完成面与面之间的完全接触，恐怕就可以将这样的固体之间的连接技术叫做粘接吧！在充填这样2个固体间空隙的过程中，胶粘剂是否能润湿被粘物，将是粘接成功的关键。     

关于丁苯橡胶和氯丁橡胶自粘界面的粘接效果

作者通过试验研究了丁苯橡胶、氯丁橡胶弹性体自粘界面的粘接效果,探讨了影响其自粘强度的因素。     

粘接界面微观结构研究

将分子自组装技术、表面配位膜技术及双组分阻蚀剂协同处理技术分别应用于一些复合材料体系,如碳纤维－ 环氧、铝－ 碳纤维增强环氧及铜－ 环氧体系等,使复合的基材和基体趋向于较佳的界面匹配,达到了理想的增强复合效果。同时,采用 Ｓ Ｅ Ｒ Ｓ、 Ｆ Ｔ－ Ｉ Ｒ、 Ｘ Ｐ Ｓ、 Ｓ Ｅ Ｍ 等多种现代表面分析手段对复合材料界面微观结构进行了研究。结果表明：含有硫和氮等极性原子的有机化合物由于其对金属的强烈的配位能力可在金属表面形成聚合物膜或吸附形成自组装结构,由此对界面有优良的阻蚀作用。调节这些化合物中的端基活性官能团可使之与胶粘剂发生偶联反应而形成牢固的界面化学键。     

Correlation between surface tension and physical paint properties

Surface tension is a parameter of decisive importance for characterizing painted and unpainted surfaces related to wetting and adhesion phenomena. Measurements of the surface tension of solids by means of an automatic contact angle measurement device are presented. The theoretical evaluations provide for a separation of the surface tension into polar and disperse components. In addition, this paper briefly touches on other more far-reaching approaches (acid/base) and discusses a method for the determination of the dynamic surface tension of liquids.     

The effect of four methods of surface activation for improved adhesion of wood polymer composites (WPCs)

Wood Polymer Composites (WPCs) have attracted a lot of interest in recent years as materials with a high renewable content. However the adhesion between WPC components is problematic because of low surface energy and the hydrophobic nature of the most widely used polymer matrices, i.e. polyolefins. Thus this paper has looked at four surface activation pretreatment methods to improve adhesion properties for bonding using epoxy adhesives, namely: hydrogen peroxide solution; hot air; a gas flame; and halogen heating lamps. The treatments were applied to WPC materials made from 60% wood flour in a polypropylene matrix, and lap joint shear strength was measured.Shear strength values showed that all treatments except the halogen heating lamps increased the bond strength and the best results were achieved with hydrogen peroxide treatment at a pH of 7.5 (37% improvement); a two pass hot air treatment at a pass speed of 75 mm s⁻¹ (44% improvement); and a gas flame treatment at a pass speed of 175 mm s⁻¹(41% improvement).The bond strength was increased to values that caused failure within the material, rather than at the interfaces of the bond line.     

Surface energy, surface topography and adhesion

In this paper are discussed some of the fundamental principles which are relevant to an understanding of the influence that interfacial roughness may have on adhesion. The surface energies of the adhesive, substrate and of the interface between them determine the extent of wetting or spreading at equilibrium. Numerical values for surface energies may be obtained either from contact angle measurements or from analysing force–displacement curves obtained from the surface forces apparatus. The extent to which the relationships, appropriate for plane surfaces, may be modified to take into account interfacial roughness are discussed. For modest extents of roughness, the application of a simple roughness factor may be satisfactory, but this is unrealistic for many of the practical surfaces of relevance to adhesive technology which are very rough, and is ultimately meaningless, if the surface is fractal in nature. Some examples are discussed of published work involving polymer–metal and polymer–polymer adhesion, where the roughness of the interface exerts a significant influence on the adhesion obtained. Roughness over a range of scales from microns to nanometres may strengthen an interface, increasing fracture energy by allowing bulk energy dissipating processes to be activated when the bond is stressed.     

Evaluation of commercially available materials to mitigate insect residue adhesion on wing leading edge surfaces

Surface contamination from insect strikes on aircraft wing leading edges can induce localized boundary layer transition from laminar to turbulent flow, resulting in increased aerodynamic drag and reduced fuel efficiency. As aviation fuel costs continue to climb, strategies to reduce fuel burn using laminar flow have led to renewed interest in surface modifications to minimize the effects of insect residue adhesion on aircraft wings. Under NASA's Environmentally Responsible Aviation Program, insect residue adhesion-resistant coatings are being studied as an approach for drag reduction. A series of aluminum alloy test surfaces were coated with commercially available materials and characterized using contact angle goniometry. The surfaces were subsequently subjected to controlled impact of crickets using a custom-built pneumatic insect delivery device. Impact events were recorded and analyzed using high-speed digital photography and characterized using optical surface profilometry. Residue adhesion was observed on all of the coatings investigated. The cricket impact event was related to liquid droplets impacting surfaces at high velocities and was analyzed as such. Coating surface energy was determined to influence residue adhesion.     

Effect of uniaxial drawing on surface chain structure and surface tension of poly(trimethylene terephthalate) film

Changes in the surface chain structure and the critical surface tension of poly(trimethylene terephthalate) (PTT) film under uniaxial drawing were examined by polarized attenuated total reflection infrared (ATR-IR) spectroscopy and contact angle measurement. It was observed from the stress-draw ratio curve and density measurement that the strain-induced crystallization occurs at the draw ratio of 2.5. From the ATR-IR spectra, it was also realized that the surface chain structure changes with the draw ratio, showing a remarkable increase in the surface crystallinity at the draw ratio between two and three. The critical surface tension of uniaxially drawn films increases with the draw ratio due to an increase in the surface crystallinity developed by the strain-induced crystallization. It is concluded that the surface properties of PTT film such as the chain structure at the surface and the critical surface tension are very closely related to the condition of uniaxial drawing.     

Wetting of fat crystals by triglyceride oil and water. 2. adhesion to the oil/water interface

Fat crystals influence the stability of food emulsions, such as margarine, butter, or cream, if adsorbed to the oil/water interface. During the adsorption process, a new fat crystal/water interface is created, while the oil/water interface is lost. The driving force for adsorption is therefore the difference between the interactions between fat crystal/water and oil/water. In this work, we have estimated this interaction difference and compared it to the displacement energy for fat crystals from the oil/water interface to the oil. Our calculations have shown that fat crystal adsorption to the oil/water interface (expressed by contact angle ϑ) is determined by polar energy, excess of fat crystal/water over oil/water (I _sw -I _ow ). The interfacial tension constitutes the resistance force for crystal adsorption to the interface. Polar interaction energy for fat crystal/water is stronger than the polar interaction energy for oil/water in all cases examined (I _sw -I _ow >0). The difference corresponds to about 10⁴–10⁶ hydrogen bonds for a hypothetical fat crystal with a diameter of 1 μm. The displacement energy for fat crystals to oil is lower than the polar energy excess in most cases examined. Thus, an additional interaction between fat crystals and oil makes it easy to displace the crystals to the oil. There is also a relationship between the adhesion tension (-γ _ow • cos ϑ) for the crystals at the oil/water interface and the interfacial tension γ _ow . A straight line of slope -1 is achieved for systems with low interfacial tensions (γ _ow ) and low polar energy excess (I _sw -I _ow ).     

Effect of surface roughness on the adhesion of electrolessly plated platinum to poly(ethylene terephthalate) films

Poly(ethylene terephthalate) films were treated with aqueous sodium hydroxide solutions of different concentrations for various times. The rate of weight loss increased with the addition of a swelling agent (methylene chloride) or a cationic surfactant. The surface roughness of the treated films was determined from atomic force microscopy (AFM) and pore diameter was obtained from scanning electron microscopy (SEM). In general, surface roughness was found to increase with increasing weight loss for the treated films. A maximum roughness was obtained for samples with a weight loss of approximately 15-20%, beyond which the roughness of the samples decreased. The addition of methylene chloride and surfactant resulted in an almost two-fold increase in the roughness for all treatment times investigated. The adhesion of electrolessly plated platinum film was dependent on the contact area produced by chemical treatment. Treatments producing smaller diameter pores of greater depth gave better adhesion.     

Studies on metal/benzocyclobutene (BCB) interface and adhesion

Interfacial characteristics such as chemical reaction, metal diffusion, and morphology were investigated for Cu/BCB, Cr/BCB and Ti/BCB structures. Using Auger and XPS depth profiling, the formation of titanium carbide and chromium oxide was confirmed at the metal/BCB interface. Annealing at 250°C for extended periods resulted in the diffusion of Cu, Cr and Ti into the BCB and subsequent formation of Cu-Si, CrSi₂ and Ti-Si compound precipitates. The reaction is a thermal diffusion controlled process which is dependent on time and temperature. Ar sputtering treatment of BCB film before metallization was found to roughen the surface, resulting in metal spikes which penetrate into the roughened BCB film. However, the peel strength of metals on BCB was only about 177 g cm^_1presumably due to the brittleness of the BCB film. The etch rates of the BCB film in a reactive ion etcher (RIE) and a plasma etcher were measured using Ar, O₂, O₂ + CF₄, and O₂ + SF₆ gas mixtures. Faster etch rates were obtained when CF₄ and SF₆ were added to oxygen, since the presence of atomic fluorine enhances the etch rate of organics, while also etching Si and SiO₂ formed by exposure of Si-containing BCB film to oxygen gas. Surface compositional changes on the BCB film were observed by XPS after plasma modification. Pure O₂ and O₂ + CF₄ plasmas oxidized the carbo-siloxane linkage (C_—Si_—O) of the BCB, resulting in the formation of SiO₂ on the surface. The O₂ + SF₆ plasma, however, did not produce the surface SiO₂, because of its faster Si and SiO₂ etch rates.     

Effect of surface free energy on the adhesion of biofouling and crystalline fouling

Pipelines and heat exchangers using seawater as coolant suffer from biofouling. Biofouling not only reduces heat transfer performance significantly, but also causes considerable pressure drop, calling for higher pumping requirements. It would be much more desirable if surfaces with an inherently lower stickability for biofouling could be developed. In this paper, a cost-effective autocatalytic graded Ni-Cu-P-PTFE composite coating with corrosion-resistant properties was applied to reduce biofouling formation. The experimental results showed that the surface free energy of the Ni-Cu-P-PTFE coatings, which were altered by changing the PTFE content in the coatings, had a significant influence on the adhesion of microbial and mineral deposits. The Ni-Cu-P-PTFE coatings with defined surface free energy reduced the adhesion of these deposits significantly. The anti-bacterial mechanism of the composite coatings was explained with the extended DLVO theory.     

Work of Adhesion as a Dominant Factor in Formation of Composition‐Gradient Thermosensitive Gel

By copolymerizing a thermosensitive primary component, N‐isopropylacrylamide (NIPA), and an ionic secondary component, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) between two substrates of hydrophilic glass and hydrophobic polytetrafluoroethylene (Teflon), a novel composition‐gradient copolymer gel, in which the AMPS content decreases gradually towards Teflon, is prepared. The formation of the composition‐gradient in NIPA‐co‐AMPS gels is discussed in terms of the work of adhesion between a solution and a substrate, i.e., the liquid‐solid interfacial free energy. The work of adhesion is determined from the Young‐Dupré equation on the basis of the measured contact angle and the surface tension in the system consisting of an aqueous solution containing NIPA or AMPS monomers or polymers and glass or Teflon as the substrate. The values of the work of adhesion of AMPS monomer and polymer on Teflon were lower than those on glass. Thus, AMPS remains relatively stable at the glass interface and unstable at the Teflon interface. This repulsion of AMPS due to the hydrophobicity of the Teflon wall generates the composition‐gradient.