铝箔／聚酰亚胺粘接界面的XPS研究

本文用Ｘ射线光电子能谱仪（ＸＰＳ），对铝箔和聚酰亚胺粘剂的粘接界面进行了较详细的研究，分析了铝箔经几种方法预处理后改性表面的化学状态和化学组成及其对粘接强度的影响，讨论了可能的粘接机理及断裂机理。     

电子胶粘剂界面弱化的机理探讨及影响因素分析

对粘接理论和界面处的微观作用力进行了讨论,并对影响电子胶粘剂界面粘接强度的关键因素进行了探讨。本文研究认为,吸附理论、互锁理论和扩散理论描述的微观作用力对电子胶粘剂的粘接具有重要贡献,而静电理论和吸盘理论描述的微观作用力可以忽略不计;界面化学组成、润湿程度、界面污染、界面形貌、温度和中间相厚度会显著影响界面粘接力。最后从上述关键因素出发,结合相关工程经验,对电子胶粘剂的界面弱化机理进行了梳理。     

激光共聚焦显微镜在牙本质粘接界面观察中的应用

先制备牙本质粘接试件,将切片打磨后使用激光共聚焦显微镜对牙本质粘接界面的自发荧光特征进行探测。不同粘接剂形成的粘接界面都表现出了特异性的自发荧光现象,不同结构区分明显。这种激光共聚焦显微镜探测自发荧光有可能成为一种新的牙本质粘接界面观察分析方法。     

双组分PU密封剂与水泥基材的粘接性能及其特征分析

以双组分PU(聚氨酯)密封剂与混凝土砂浆基材的粘接强度作为考核指标,探讨了不同养护温度、界面干湿条件等对PU密封剂/混凝土砂浆基材粘接性能的影响,并对其粘接机制进行了分析,解释了不同养护条件所带来的试验结果的差异性。结果表明:温度、不同干湿界面对双组分PU密封剂的粘接拉伸强度有较大的影响,在使用过程中应尽量避免潮湿界面和低温环境。     

固体火箭发动机粘接界面力学性能的有限元计算及参数分析

基于界面粘接模型假设,采用界面共节点有限元分析方法,计算了粘接系统的应力与应变分布,探讨了各层材料性能参数和结构参数对粘接系统力学性能的影响。结果表明,随着衬层弹性模量增加,应力集中程度严重;绝热层的弹性模量对粘接系统的力学性能影响很小,衬层厚度对应力、应变的分布基本没影响;中间相模量和厚度是影响界面粘接质量的主要因素。高的中间相弹性模量和厚度会使应力集中程度增强,使粘接破坏更趋于内聚破坏而不是界面破坏。合理的中间相参数可改善粘接系统的粘接质量。     

衬层预固化程度对衬层/推进剂界面粘接性能的影响

研究了壳体粘接式固体火箭发动机装药中衬层的固化程度对推进剂和衬层间界面粘接性能的影响,采用红外光谱技术对衬层固化过程中微观结构的变化进行了表征,初步探讨了衬层固化程度影响界面粘接强度的机理。结果表明,衬层固化0~8h,-NCO含量迅速下降,衬层与推进剂界面的粘接强度随衬层固化时间的增加而增大;固化8~40h时,衬层中的-NCO含量下降速度减小;衬层与推进剂界面的粘接强度随衬层固化时间的变化不大。     

胶粘剂的粘弹性与粘接强度

一、前言 我们用胶粘剂使同种或异种材料接合,在完成粘接接合的状态中,在粘接界面或许有分子间力作用,或根据情况形成共价键,由此呈现粘接整体的力学强度,但要直接测定粘接界面二个物体间相互的拉力实质上几乎不可能。在实际的粘接试验中,至少在进行了具有实用意义的某种粘接后,粘接面决不会产生清晰的界面破坏。其次,按粘接试验条件的不同,其破坏形态通常也各不相     

用X射线光电子谱(XPS)法研究粘接配位键机理

本文用X射线光电子谱(XPS)法对环氧胶和被粘物(钢和氧化铝)粘接界面各元素的化学状态进行了研究。结果表明:界面处元素N、O、Fe、Al发生了化学位移,从而证实了粘接界面配位键的存在。     

表面处理对热硫化硅橡胶粘接性能的影响

采用低温等离子体对热硫化型硅橡胶表面进行处理,研究了介质气体、处理时间以及存放时间对硅橡胶表面化学状态,以及硅橡胶与端羟基聚丁二烯聚氨酯(HTPBPU)胶粘剂界面粘接性能的影响。研究结果表明,经等离子体处理后的硅橡胶表面有新官能团生成,与聚氨酯胶粘剂的界面粘接性能得到显著提升;介质气体的类型、处理时间和存放时间的长短对界面粘接性能影响不大。     

扫描电镜和X射线能量色散谱仪在涂层脱落现象分析中的应用

通过对某型ZM5铸造镁合金产品表面防热涂层脱落实际案例的分析,介绍了扫描电镜(SEM)和X射线能量色散谱仪(EDS)在该类现象分析中的应用方法.在该案例的分析中,首先使用SEM对涂层脱落界面分别进行低倍和高倍显微形貌观察,确定脱落界面的位置以及各区域的粘接情况.而后利用EDS对脱落界面的粘接异常位置与粘接正常位置的表面元素成分进行分析.最终确定脱落界面上粘接异常位置过高的硫元素含量是导致涂层脱落的原因,而硫源自镁合金氧化处理槽液中硫酸镁的残留.     

Contribution of Colloidal Forces in Non-contact Area to the Adhesion Between a Micro-probe and a Substrate Surface: Theoretical Analysis

Colloidal forces outside the microscopic probe (particle)–substrate adhesion contact area were analyzed theoretically. Equations describing the van der Waals, electrical double layer, and hydrophobic forces were derived for the non-contact area of a probe–substrate system assuming a simple sphere–flat geometry. Two cases were considered: particles freely resting on the substrate surface and particles pulling off the substrate. The results of modeling presented in this communication suggest that the adhesion of fine particles (microscopic and sub-microscopic particles) to flat surfaces can be affected by the forces acting outside the contact area. However, due to increased distance between the particle and substrate during separation, both the van der Waals and electrostatic forces acting outside the contact area are negligibly small compared to the short-range adhesion forces and they do not contribute to the measured pull-off force to any great extent for most systems. On the contrary, our calculations suggest that the long-range hydrophobic forces can contribute to the strength of adhesion between hydrophobic fine particles and hydrophobic substrates.     

粗糙度对彩色涂层与基体间附着力的影响

研究粗糙度对基体和涂层之间的附着力的影响,其一,是因为基体表面的凸凹不平导致漆膜在其上附着时产生互相咬合的现象,增大了附着力;另外,基体表面粗糙度越大其真实表面积越大,在基体表面发生腐蚀时腐蚀产物不易扩散,因此涂层附着力不易下降。     

WHEN LESS IS MORE: EXPERIMENTAL EVIDENCE FOR TENACITY ENHANCEMENT BY DIVISION OF CONTACT AREA

Most recent data on hairy systems demonstrated their excellent adhesion and high reliability of contact. In contrast to smooth systems, some hairy systems seem to operate with dry adhesion and do not require supplementary fluids in the contact area. Contacting surfaces in such devices are subdivided into patterns of micro- or nanostructures with a high aspect ratio (setae, hairs, pins). The size of single points gets smaller and their density gets higher as the body mass increases. Previous authors explained this general trend by applying the JKR theory, according to which splitting up the contact into finer subcontacts increases adhesion. Fundamental importance of contact splitting for adhesion on smooth and rough substrata has been previously explained by a very small effective elastic modulus of the fibre array. This article provides the first experimental evidence of adhesion enhancement by division of contact area. A patterned surface made out of polyvinylsiloxane (PVS) has significantly higher adhesion on a glass surface than a smooth sample made out of the same material. This effect is even more pronounced on curved substrata. An additional advantage of patterned surfaces is the reliability of contact on various surface profiles and the increased tolerance to defects of individual contacts.     

WHEN LESS IS MORE: EXPERIMENTAL EVIDENCE FOR TENACITY ENHANCEMENT BY DIVISION OF CONTACT AREA

Most recent data on hairy systems demonstrated their excellent adhesion and high reliability of contact. In contrast to smooth systems, some hairy systems seem to operate with dry adhesion and do not require supplementary fluids in the contact area. Contacting surfaces in such devices are subdivided into patterns of micro- or nanostructures with a high aspect ratio (setae, hairs, pins). The size of single points gets smaller and their density gets higher as the body mass increases. Previous authors explained this general trend by applying the JKR theory, according to which splitting up the contact into finer subcontacts increases adhesion. Fundamental importance of contact splitting for adhesion on smooth and rough substrata has been previously explained by a very small effective elastic modulus of the fibre array. This article provides the first experimental evidence of adhesion enhancement by division of contact area. A patterned surface made out of polyvinylsiloxane (PVS) has significantly higher adhesion on a glass surface than a smooth sample made out of the same material. This effect is even more pronounced on curved substrata. An additional advantage of patterned surfaces is the reliability of contact on various surface profiles and the increased tolerance to defects of individual contacts.     

Effect of the aspect ratio of the pre-existing rectangular adhesion failure on the structural integrity of the adhesively bonded single lap joint

Non-linear three dimensional (3-D) finite element analyses (FEA) of the single lap joints (SLJs) having pre-existing rectangular adhesion failure in the interface of the strap adherend and the adhesive have been carried out. The effect of the size, the shape and the aspect ratio of the pre-existing rectangular adhesion failure on (i) the strength, (ii) the interfacial stresses and (iii) the strain energy release rates (SERRs) in the vicinity of the adhesion failure front have been presented in this research work. The SLJ is subjected to uniformly applied tensile load. The adherends are made with very high strength steels and the adhesive is a commercially available AV119. The analyses of the adhesion failure propagation have been carried out by sequentially releasing the constraints of the nodes ahead of the pre-existing adhesion failure front in finite element model. The SERR values in the vicinity of the adhesion failure fronts are computed using the virtual crack closure technique (VCCT) for assessment of the structural integrity of the SLJ. The strength of the SLJ, the interfacial stresses, and the three modes of strain energy release rates (SERRs) have been found to be significantly affected by the shape and size of adhesion failures. The SERRs and interfacial stresses along the rectangular adhesion failure front are compared with the corresponding values around the circular adhesion failure front of same area, pre-existing in the SLJ. It is observed that the circular and rectangular adhesion failures of the same area will have dissimilar growth rate and the mode II is the dominant failure mode. The total strain energy release rate and the failure strength, computed from the 3-D FEA of the SLJ is in good agreement with the experimental fracture toughness of the AV119 adhesive and the experimentally obtained failure loads, respectively.     

Morphological Factors Involved in Adhesion of Acid-Cleaned Diatom Silica

Purpose

Diatoms, unicellular microalgae with silica cell walls, have strong adhesive properties, which are dominated by chemical interactions between secreted organic material and the substrate. Possible technological applications of diatoms are likely to involve the adhesion of silica particles, or derivatives, which have been cleaned of organic material. Because the morphologies of diatom cell walls are far more complex than defined model structures, the relationship between morphology and adhesion for such materials is unknown.

Methods

In this paper we develop a new approach to monitor the adhesion of acid-cleaned diatom silica using parallel-plate flow chambers. We have evaluated factors such as settling time, extent of dryness, and substrate properties, and compared diatom species with silica features differing in size, shape, and percentage of surface contact area.

Results

Results indicated better adhesion of particles with higher surface contact area below a threshold of overall size, and a contribution by the number of possible contact surfaces to initial adhesion. We identified two stages in adhesion response to increasing shear stress. In the first stage, at low shear stress, species-dependent morphology played a major role in determining the strength of adhesion. After loosely adhered particles were removed at low shear, a second stage of persistent adhesion emerged at higher shear stresses. In the second stage, variations in morphology had a much smaller effect on adhesion.

Conclusions

These results identify conditions and fundamental morphological features for adhesion that can be utilized in future technological applications of silica particles with complex shapes.     

Surface chemistry and adhesion

Adhesion science is still a controversial area of research; no universal theory of adhesion exists and the actual mechanism of adhesion operating across many industrially important interfaces is still unresolved. In this review wetting processes and methods for estimating the surface free energy of polymers from contact-angle measurements are discussed. Emphasis is placed on the relationship between the work of adhesion estimated from surface free energies of solids and the measured adhesive joint strength.     

Adhesion characterization of protective organic coatings by electrochemical impedance spectroscopy

Adhesion is considered in many situations to be a very important property of organic coatings for corrosion protection and much scientific work is devoted both to the study of the mechanism involved in polymer-metal adhesion and to the ways of measuring this property. The large number of experimental methods in existence to obtain information on coating adhesion is an indication of both the scientific and the technological interests in this material science and engineering area, but it is also a consequence of the difficulty in measuring adhesion in a general sense. As a partial alternative to the traditional adhesion measurement approaches for organic coatings, the evaluation of adhesion by electrochemical techniques such as electrochemical impedance spectroscopy (EIS) is discussed for different examples. The influences on adhesion of different pretreatments or organic coatings are discussed, considering aluminium, galvanized steel, and stainless steel substrates, and we have shown that the information obtained by using an electrochemical approach can be used for adhesion evaluation, with particular attention to the monitoring of adhesion in an aqueous environment, which is the most detrimental for protective organic coatings.