Comparative study of pineapple leaf microfiber and aramid fiber reinforced natural rubbers using dynamic mechanical analysis

Natural fiber is often considered inadequate for high performance reinforcement of polymer matrix composites. However, some natural fibers have relatively high mechanical properties with modulus close to that of high-performance synthetic fibers. Since the reinforcing efficiency of a short fiber is determined not only by the fiber modulus, but also by other physical properties such as the length to diameter ratio. Here it is shown, for the first time, that pineapple leaf fiber, whose modulus is somewhat lower than that of aramid fiber, can be used to reinforce natural rubber more effectively than aramid fiber. The situation was achieved by breaking down the fiber bundles into the constituent microfibers to gain very high aspect ratio. Comparisons were made at fiber contents of 2, 5 and 10 parts (by weight) per hundred of rubber (phr) using dynamic mechanical analysis over a range of temperature. The results reveals that at temperature below the glass transition of the matrix rubber and low fiber contents of 2 and 5 phrs, aramid fiber displays slightly better reinforcement efficiency. At high temperatures of 25 and 60 °C and high fiber content of 10 phr, pineapple leaf microfiber clearly displays higher reinforcement efficiency than does aramid fiber. Surface modification of the fiber by silane treatment provides a slight improvement in reinforcing efficiency.     

Synergy effects of multi-walled carbon nanotube and graphene nanoplate filled epoxy adhesive on the shear properties of unidirectional composite bonded joints

In this paper, multi-walled carbon nanotubes (MWCNTs) and graphene nanoplates (GNPs) were dispersed into epoxy adhesive by sonication method to investigate their synergy effects on the shear properties of unidirectional composite bonded single lap joints (SLJs). The effect of the viscosity of epoxy resin and hardener on the dispersion process was studied. Testing results showed that the incorporation of MWCNTs and GNPs significantly improved the shear strength and elongation of SLJs at failure. 0.75 wt% MWCNTs/GNPs hybrids reached the highest enhancement of shear strength and elongation by 36.6% and 33.2%, respectively. In addition, the thermal stability of epoxy adhesive was improved by nanofillers in some extent. Finally, the failure mode of SLJs and fracture surfaces of the bonding area as well as the damage mechanism of nanofillers were analyzed.     

Evaluation of adhesion between glass/epoxy composite substrate and copper foil for printed circuit board applications

Adhesion between glass/epoxy composite substrate and copper foil was evaluated by 90° peeling test. Effect of fracture behavior and the peel strength on copper foil style was experimentally investigated using copper foils with various surface roughness. As mechanical anchoring effect increases with increased surface roughness, the surface roughness increased the surface roughness of copper foil strongly affected the peeling strength and local load variation during the test. The fracture behavior was characterized by secondary electron image and reflective electron image techniques of scanning electron microscopy (SEM). All of the specimens were found to fracture at the anchor points formed in the resin layer on the surface of the substrate. The experimental results were correlated to a formulation based on the theory of beams on elastic foundation, which is presented for predicting the adhesive strength in the adherend- adhesive system. In order to apply this formulation to a no adhesive system, such as FR-4/copper foil, an analytical model was proposed. In this model, a mixture phase of the copper with the surface resin in the substrate was regarded as the adhesive. The calculated results were in relatively good agreement with the experimental results. It was confirmed that the analysis model and evaluation method is useful to predict the peel strength due to the mechanical anchoring effect.     

Peeling of an elastic membrane tape adhered to a substrate by a uniform cohesive traction

An analytical model is provided for the peeling of a tape from a surface to which it adheres through cohesive tractions. The tape is considered to be a membrane without bending stiffness and is initially attached everywhere to a flat rigid surface. The tape is assumed to deform in plane strain, and finite deformations in the form of elastic strains are accounted for. The cohesive tractions are taken to be uniform when the tape is within a critical interaction distance from the substrate and then to fall immediately to zero once this critical interaction distance is exceeded. When the distance between the tape and the substrate is zero, repulsive and attractive tractions balance to zero; in this segment, sliding of the tape relative to the substrate is forbidden when we pull the tape up somewhere in the middle, though we permit such sliding when the tape is peeled from one end. In the cohesive zone and where the tape is detached, the interaction of the tape with the substrate is frictionless. Results are given for the force to peel a neo-Hookean tape at any angle up to vertical when one end of it is pulled away from the substrate, as well as for scenarios when the tape is lifted somewhere in the middle to form a V shape being pulled away from the substrate.     

ITO films on glass substrate by sol–gel technique: synthesis,characterization and optical properties

The present paper extensively demonstrates synthesis, characterization and optical properties of semiconductor indium tin oxide (ITO) thin films on glass substrate using sol–gel technique for gas sensor applications. Turbidity, pH values, wettability and rheological properties of the prepared solutions were measured to determine solution characteristics by turbidimeter, pH meter, contact angle goniometer and rheometer machines prior to coating process. Thermal, structural, microstructural, mechanical and optical properties of the coatings were characterized by differential thermal analysis–thermogravimetry (DTA/TG), fourier transform infrarared, X-ray diffraction (XRD), scanning electron microscopy, scratch tester, refractometer and spectrophotometer. Four different solutions were prepared by changing solvent concentration. Turbidity, pH, contact angle and viscosity values of the solutions were convenient for coating process. Glass substrates were coated using the solutions of InCl₃, SnCl₂, methanol and glacial acetic acid. The obtained gel films were dried at 300 °C for 10 min and subsequently heat-treated at 500 °C for 10 min in air. The oxide thin films were annealed at 600 °C for 60 min in air. DTA/TG results revealed that endothermic and exothermic reactions are observed at temperature between 70 and 560 °C due to solvent removal, combustion of carbon based materials and oxidation of Sn and In. The spectrum of ITO precursor film annealed at 500–600 °C shows an absence of absorption bands corresponding to organics and hydroxyls. In₂Sn₂O_7−x phase was dominantly found as well as SnO₂ with low intensity from XRD patterns. It was found that surface morphologies of the film change from coating island with homogeneous structures to regular surface and thinner film structures with increasing solvent concentration. The films prepared from the solutions with 8 mL methanol have better adhesion strength to the glass substrate among other coatings. Refractive index, thickness and band gap of ITO thin films were determined to be 1.3171, 0.625 μm and 3.67, respectively.     

附着性能优异的碳对电极的制备及其在染料敏化太阳能电池中的应用

通过引入一种低成本商业导电碳浆(CC)作为粘结剂, 以色素碳黑(Cb)作为催化材料, 成功制备了Cb-CC对电极. 着重解决传统碳对电极的主要问题, 即碳与导电基底的附着力问题. 附着力测试结果表明: CC的引入改善了Cb与导电基板之间的附着力, 同时增强了碳对电极的导电性和稳定性. 扫描电镜(SEM)结果显示, CC与Cb混合后, 碳膜的多孔结构依然存在, 即这种对电极能同时增加导电性和催化活性. 采用循环伏安(CV)和电化学阻抗谱(EIS)对Cb-CC对电极的催化活性进行了研究. 光电性能测试结果表明, 基于Cb-CC染料敏化太阳能电池(DSSC)的能量转换效率达到了6.54%, 进一步优化后, 当Cb和CC的质量比为23:77 时效果最佳, 达到最高效率6.81%. 此外, 基于Cb-CC的DSSC长期稳定性测试结果表明, 700 h后各项光电参数无明显下降. 该实验成果为增强整体电池的稳定性和促进低成本DSSC产业化奠定了基础.     

Role of acid–base interactions on the adhesion of oral streptococci and actinomyces to hexadecane and chloroform—influence of divalent cations and comparison between free energies of partitioning and free energies obtained by extended DLVO analysis

Calcium is an abundantly present, divalent cation in the oral cavity and plays a crucial role in the adhesion of oral microorganisms to tooth surfaces as well as in coaggregation and coadhesion among the oral microflora. The aim of this study was to determine the effects of divalent cation (Ca²⁺, Mg²⁺, Ba²⁺) adsorption on the adhesion of two actinomyces and two streptococcal strains to hexadecane (MATH) and chloroform (MATS) in order to detect changes in acid–base character of the cell surfaces. Initial removal rates of the organisms by hexadecane, lacking an acid–base interaction with the organisms, were always smaller than those by chloroform. Furthermore, adsorption of divalent cations generally increased the initial removal rates of the microorganisms, but no statistically significant differences among different cations were observed. Gibbs energies of partitioning calculated from the stationary end-point adhesion of the organisms ranged from −2 to −4 kT for adhesion to hexadecane and were about twofold more negative for adhesion to chloroform. Contact angles on lawns of microorganisms with and without adsorbed divalent cations were similar. Zeta potentials of all microorganisms were slightly negative under the conditions of MATH and MATS and became only 4 mV more positive upon divalent cation adsorption. Hexadecane had a zeta potentials of −21 mV in the potassium phosphate solution used, which became 13 mV less negative upon Ca²⁺ adsorption. An extended DLVO approach of microbial adhesion to hexadecane, based on microbial contact angles and zeta potentials, taking into account Lifshitz–van der Waals, acid–base and electrostatic interactions did not show any potential energy barrier and demonstrated a deep primary interaction minimum at close approach due to acid–base attraction. As the Gibbs energy of partioning was only −2 to −4 kT, it is concluded that for the collection of organisms studied here, the final contactable surface area is small and structural features on the cell surfaces like fibrils and fimbriae, maintain a distance of ca. 10–15 nm between the hexadecane and the overall cell surface and therewith prevent acid–base interactions to become operative to a significant extend. Furthermore, from the lack of influence of divalent cations on macroscopic cell surface contact angles and zeta potentials, it is suggested that cation adsorption is minor and localized to the fibrils and fimbriae.     

The effect of nitrogen and oxygen plasma on the wear properties and adhesion strength of the diamond-like carbon film coated on PTFE

Diamond-like carbon (DLC) films were deposited on polytetrafluoroethylene (PTFE) using a radiofrequency plasma chemical vapour deposition method. Prior to DLC coating, the PTFE substrates were modified with O₂ and N₂ plasma to enhance the adhesion strength of the DLC film to the substrate. The effect of the plasma pre-treatment on the chemical composition and the surface energy of the plasma pre-treated PTFE surface was investigated by X-ray photoelectron spectroscopy (XPS) and static water contact angle measurement, respectively. A pull-out test and a ball-on-disc test were carried out to evaluate the adhesion strength and the wear properties of the DLC-coated PTFE.In the N₂ plasma pre-treatment, the XPS result indicated that defluorination and the nitrogen grafting occurred on the plasma pre-treated PTFE surface, and the water contact angle decreased with increasing the plasma pre-treatment time. In the O₂ plasma pre-treatment, no grafting of the oxygen occurred, and the water contact angle slightly increased with the treatment time. In the pull-out test, the adhesion strength of the DLC film to the PTFE substrate was improved with the plasma pre-treatment to the PTFE substrate, and N₂ plasma pre-treatment was more effective than the O₂ plasma pre-treatment. In the ball-on-disc test, the DLC film with the N₂ plasma pre-treatment showed good wear resistance, compared with that with O₂ plasma pre-treatment.     

Electrode contact study for SiGe thin film operated at high temperature

A study on the electrode contact of the sputtered SiGe thin film is reported for application of devices working at high temperature. Surface morphological characterization with optical microscope and AFM (atomic force microscope) together with the electrical characterization by TLM measurements (transmission line method) were performed before and after aging at 500 °C for 24 h using various sputtered multilayer electrodes, Ti/Au/Ti, Ta/Pt/Ta and Ti/Pt/Ti, on 300-nm B-doped SiGe thin film deposited by magnetron sputtering and furnace crystallisation at high temperature. After aging at 500 °C for 24 h, the Ti/Au/Ti multilayer electrodes seriously degraded to be non-ohmic contact, showing rough surface morphology. The Ti/Pt/Ti metal layers showed the lowest specific contact, resistivity before and after aging, 1.46 × 10⁻³ Ω cm² and 1.68 × 10² Ω cm² respectively.     

Mechanical and Adhesive Properties of Ploy(ethylene glycerol) Diacrylate Based Hydrogels Plasticized with PEG and Glycerol

Using polyethylene glycol(PEG) or glycerol as the plasticizer, we synthesized the hydrogels from poly(ethylene glycol) diacrylate(PEGDA), polyvinylpyrrolidone(PVP) and poly(vinyl alcohol)(PVA) under UV radiation. The effects of different plasticizers on the mechanical properties and adhesion properties of the hydrogels were investigated. The results show that the plasticizer can improve the elongation and peeling force. The most pronounced changes in the tensile property of the hydrogels are due to the addition of glycerol followed by PEG, the lower the plasticizer's molecular weight, the greater its effect. The maximum peeling force is 0.317 or 0.257 N with PEG or glycerol as plasticizer, respectively, and their adhesion properties are due to the formation of hydrogen bonds.