热蒸发YbF3薄膜的机械特性

 实验研究了热蒸发YbF₃薄膜在大气中的应力和附着力。利用Veeco干涉仪,测试了各种工艺条件下单层YbF₃薄膜的应力。结果发现:YbF₃薄膜的残余应力为张应力,热应力在残余应力中的比重较大;沉积方式对薄膜应力的影响不大;薄膜应力在大气中有一个释放的过程。热处理后,YbF₃薄膜应力增大。     

Hydrophobic surfaces of spin-assisted layer-by-layer assembled polyelectrolyte multilayers doped with copper nanoparticles and modified by fluoroalkylsilane

Polyelectrolyte multilayers (PEMs) fabricated by spin-assisted layer-by-layer assembly technique were used as nanoreactors for in situ synthesis of Cu nanoparticles, allowing generation of Cu nanoparticles doped composite, denoted as Cu-nanoparticles PEMs. Thus chemical reaction within the PEMs was initiated by a series of reaction cycles in which Cu²⁺ was absorbed into the polymer-coated silicon substrate and reduced in NaBH₄ solution. The surface of Cu-nanoparticles PEMs was modified by heptadecafluorodecyl-trimethoxysilane (FAS-17) with low surface energy, generating a hydrophobic film. The adhesion and nano-friction behavior of the hydrophobic film was investigated using an atomic force microscope, while its macro-tribological behavior sliding against stainless steel under dry- and distilled-water-lubricated conditions was investigated using a UMT-2 test rig. It was found that Cu-nanoparticles PEMs modified with FAS-17 has a lower friction and higher adhesion than that without modification. Moreover, the hydrophobic film possesses lower friction coefficient under water-lubrication and higher friction coefficient under dry-sliding than the hydrophilic film under the same conditions, which could be mainly due to the difference in the surface energy. The titled hydrophobic films with low adhesion and friction would have potential application in micro/nano-electro-mechanical systems.     

The use of contact angle measurements to estimate the adhesion propensity of calcium carbonate to solid substrates in water

We have studied a series of solids using contact angle measurements; stainless steel, gold, aluminium, titanium nitride and PTFE that are frequently used in domestic water environments. It was found the influence of electron-donor (γ⁻) and electron-acceptor (γ⁺) free energies on material scaling rate was dominated by water wetting angles, providing materials exhibit an average roughness below 100 nm. The γ⁻ component had the greatest influence on theoretical adhesion, while γ^LW, (Lifshitz-van der Waals) γ⁺ and γ^AB (acid-base) had little effect. From the materials analysed, amorphous carbon coatings were least adhesive, while ‘kettle coating’ and highly roughened steel the most adhesive. The size and distribution of asperities also influenced the polar free energies and subsequent adhesion due to fluctuations in the wetting angle. The results obtained indicate works of adhesion can be used as a complementary technique with Lewis acid-base theory to deliver useful information about the propensity of scale to deposit on solids.     

A phase field model for vesicle–substrate adhesion

In this paper, a phase field model is developed for vesicle adhesion involving complex substrate and vesicle geometries. The model takes into account an adhesion potential that depends on the distance of vesicle to the substrate. A variational problem is solved in a 3D computational domain by minimizing the contribution of bending elastic energy and the adhesion energy under the constraints of total surface area and volume, described via a phase function. An adaptive finite element method is used to efficiently compute the numerical solutions of the model. The computational results are validated through comparison of several axisymmetric shapes with the sharp-interface ODE solution. Moreover, we compute shapes for non-axisymmetric situations to support the observation that concave substrates favor adhesion.     

Structure and adhesion of MoSi2/Ni interfaces: Evaluation of MoSi2 as an alternative bond coat alloy

We use density functional theory to evaluate the stability of molybdenum disilicide coatings on a nickel substrate, as a possible bond coat alloy for high temperature coating applications. We consider the MoSi₂(0 0 1)/Ni(1 1 1), MoSi₂(1 0 0)/Ni(1 1 1), and MoSi₂(1 1 0)/Ni(1 1 1) interfaces and predict quite strong (3.5-3.8 J/m²) adhesion of this metal-silicide ceramic to nickel. The origin of this strong adhesion is elucidated by examining the geometric and electronic structure of the interfaces. We predict that Mo and Si atoms at the interface primarily occupy Ni 3-fold hollow sites, the typical adsorption site on Ni(1 1 1). Projected local densities of states and electron density difference plots reveal a mixture of localized, covalent Si-Ni bonds and more delocalized metallic Mo-Ni bonding, as the origin of the strong interfacial bonding. As emphasized in our earlier work, creation of strong covalent bonds at interfaces results in very strong adhesion. Such strong adhesion makes MoSi₂ a potential candidate for use in thermal barrier applications, in conjunction with a yttria-stabilized zirconia topcoat.     

Small size plasma tools for material processing at atmospheric pressure

A small size radiofrequency plasma jet source able to produce cold plasma jets at atmospheric pressure is presented. The surface modification of polyethylene terephtalate, polyethylene and polytetrafluorethylene foils is performed by using a scanning procedure. The contact angle measurements reveal that the treatment leads to hydrophilicity increase. The roughening of surface, specific to each material is noticed. A significant improvement of adhesion is obtained as result of atmospheric plasma treatments.     

Nucleation and growth of cavities in soft viscoelastic layers under tensile stress

The process of growth of an individual cavity in a viscoelastic adhesive layer has been investigated experimentally. The formation of cavities was caused by the application of a negative pressure on a very confined layer with a flat-ended probe. The cavities appeared in the bulk of the adhesive layer and were observed for a range of values of applied stress approximately ten times higher than the shear modulus of the adhesive layer. Depending on the loading rate, the shape of the growing cavity changed from a flat disc to a more spherical shape. Furthermore, the growth rate of the cavity radius was consistent with a constant strain rate at the edge of the cavity, which suggests a constant level of stress at the edge of the cavity. Received 5 June 2002 RID="a" ID="a"Current address: Ethicon, Johnson & Johnson, Route 22 West, P.O. Box 151, Somerville, NJ 08876-0151, USA. RID="b" ID="b"e-mail: costantino.creton@espci.fr     

The influence of preparative parameters on the adhesion of alumina washcoats deposited on metallic supports

Well-adhered alumina washcoats on FeCrAl metallic supports were prepared using boehmite sols and alumina slurries. The microstructure and the surface performance of the washcoat/support were investigated by SEM, XRD, and ultrasonic vibration. The effects of the main preparative parameters on the coating adherence were studied. The optimal coating conditions are presented as follows: pre-oxidation of the metallic supports was performed at 900 °C for 10 h, the sol layer loadings were 2.0-6.6 wt.%, and the slurry layer loadings were less than 25.3 wt.%. The sol layer drying was performed at 30 °C for 1 h and that for the slurry layer the drying was performed at 120 °C for 2 h, and the coating calcining was performed at 900 °C for 2 h. The SEM photographs of coated samples show that alumina washcoats were well deposited on the metallic supports.     

A nanoscale understanding of the adhesion of polybutylene terephthalate on aluminum

The adhesion strength of polybutylene terephthalate (PBT) on aluminum was investigated using density functional theory-based total energy calculations. Aluminum atom was connected to a PBT monomer at different orientations and total energies were calculated in order to determine the most stable orientation. The energy differences showed that the Al oriented at 180° with the ester group of the monomer bonded strongly. Using this orientation, the PBT monomer-adhesion on aluminum surface and the aluminum atom adhesion on PBT bulk were also investigated.     

溶有增粘树脂的丙烯酸酯乳液共聚及压敏胶的性能

用一步法将溶有松香或氢化松香的丙烯酸酯单体进行乳液共聚合时，由于增粘树脂分子的自由基链转移作用使单体的转化率明显降低．先将大部分丙烯酸酯单体进行乳液共聚制得种子乳液，再将溶有增粘树脂的剩余丙烯酸酯单体加到种子乳液中进行第二步乳液共聚合，可显著提高单体的总转化率．用ＴＥＭ对分步聚合所得复合乳液的粒子形态进行了观察并对第二步乳液共聚合的机理进行了讨论．用分步乳液共聚合的方法制得的增粘树脂 丙烯酸酯复合乳液共聚物的压敏胶粘性能较一步法有很大的提高．