Oxygen plasma processing and improved interfacial adhesion in PBO fiber reinforced epoxy composites

The effects of oxygen plasma processing on the improved interfacial adhesion properties of poly(1,4-phenylene-cis-benzobisoxazole) (PBO) fiber reinforced epoxy composites have been investigated in this paper. Both As-spun (AS) and high-modulus (HM) PBO fiber systems were studied. The characterization techniques included microscopy, surface analysis, and composite interfacial adhesion tests. The results showed that the high-modulus fiber surface free energy could be increased significantly by 42.2% from 46.2 to 65.7 mJ/m², while the tensile strength was only slightly decreased by 3.4% from 5.87 to 5.67 GPa. In addition, the interfacial adhesion strength of PBO fiber reinforced epoxy composite was improved by 37.5% from 32.5 to 44.7 MPa for the HM fiber system. The improvement has been attributed to the enhanced cohesive failure that dissipated more fracture energy.     

The Auger analysis of contaminants that influence the thermocompression bonding of gold

Thin layers of metallic impurities and hydrocarbon residues on the surface of gold-plated headers and lead frames were found to degrade the mechanical strength of thermocompression bonds used for attaching wire leads. Any contamination of the lead wire or of the gold on the header or lead frame can prevent intimate gold-to-gold contact and result in unreliable bonding. These impurities can codeposit from solution during plating and can then segregate to the surface during thermal processing or can diffuse through the gold from the back side. At the surface, the metals oxidize and act as barriers to contact between the gold wire and the plated metal surface.Such impurities are often present in submonolayer quantities which preclude detection by most analytical techniques other than Auger and X-ray photoelectron spectroscopy (XPS). Both these analytical techniques can be used to study the surface composition to a depth of three or four monolayers with a bulk sensitivity of about 0.1 at.%. Surface concentrations of Fe, Ni, Cu, Ag, Si and other metals were observed in the 1–5 at.% range. This is attributed to the fact that, for example, 100 ppm Ni in the bulk of an Au film 5000 Å thick represents 10 at.% if it diffuses to the surface. Recent results indicate that the composition of the plating bath as determined by emission spectroscopy can be sorrelated with the surface composition and subsequently the thermocompression bondability. This information can be used to establish the maximum tolerable impurity levels in the Au plating bath.     

Hierarchical poly(p-phenylene benzobisoxazole)/graphene oxide reinforcement with multifunctional and biomimic middle layer

A new hierarchical reinforcement developed by coating biomimic polydopamine (PDA) on the surface of poly(p-phenylene benzobisoxazole) (PBO) fibers, which served as a platform for the graphene oxide (GO) grafting, using branched polyethyleneimine (b-PEI) as a bridging agent. The surface morphologies and chemical structures of PBO fibers were characterized for confirming the formation of covalent bond between GO and PBO fibers. The surface roughness (R_a) and wettability of the obtained fibers, denoted as PBO@PDA-PEI-GO, were obviously increased in comparison with those of untreated one. The reinforcement offered a 68.8% enhancement in the interfacial shear strength (IFSS) without degrading the base fiber. The PDA layer on the PBO fiber surface led to improved UV resistance. The hydrothermal aging resistance of PBO/epoxy composite was also greatly improved. This biomimic surface modification approach is facile to prepare, highly efficient to enhance interface, adaptable to all high-performance fibers, and meaningful in multifunctional applications.     

Cu/ n2TiO 2/ PBO复合纤维的制备

以 PBO纤维为基体 , 采用浸渍涂覆法在 PBO纤维表面包覆纳米 TiO 2膜 , 采用化学镀法将 Cu沉积到纳米 TiO 2膜表面 , 制备了 Cu/ n2 TiO 2/ PBO复合纤维 , 研究了影响纳米 TiO 2沉积速率和 Cu 沉积速率的主要因素。结果表明 , 纳米 TiO 2与偶联剂的浓度配比是影响纳米 TiO 2包膜形成的主要因素 , 当纳米 TiO 2与偶联剂浓度配比为 1∶1. 2时 , 制备的 n2TiO 2/ PBO复合纤维界面结合力较好 , 且纳米 TiO 2包覆层比较均匀。影响化学镀铜- 1 的主要因素有镀液成分、 反应时间和反应温度。在镀液成分的浓度配比为 CuSO 4·5H 2O 12 g ·L 、KNaC 4H 4 - 1 - 1 - 1O 68 g·L 、HCHO 6 mL ·L 和 NaOH 10 g·L , 反应温度 50℃, 镀铜时间 20 min的条件下 , 制备了负载均匀 , 界面结合力较好的 Cu/ n2 TiO 2/ PBO复合纤维。     

Metallization of Kevlar fibers with gold

Electrochemical gold plating processes were examined for the metallization of Kevlar yarn. Conventional Sn(2+)/Pd(2+) surface activation coupled with electroless Ni deposition rendered the fibers conductive enough to serve as cathodes for electrochemical plating. The resulting coatings were quantified gravimetrically and characterized via adhesion tests together with XRD, SEM, TEM; the coatings effect on fiber strength was also probed. XRD data showed that metallic Pd formed during surface activation whereas amorphous phases and trace amounts of pure Ni metal were plated via the electroless process. Electrodeposition in a thiosulfate bath was the most efficient Au coating process as compared with the analogous electroless procedure, and with electroplating using a commercial cyanide method. Strongly adhering coatings resulted upon metallization with three consecutive electrodepositions, which produced conductive fibers able to sustain power outputs in the range of 1 W. On the other hand, metallization affected the tensile strength of the fiber and defects present in the metal deposits make questionable the effectiveness of the coatings as protective barriers.     

Atmospheric air plasma treated PBO fibers: Wettability,adhesion and aging behaviors

Poly (p–phenylene-2, 6-benzobisoxazole) (or PBO) fibers were modified by air dielectric barrier discharge plasma (air-DBD) with different treatment time. The wettability of the PBO fibers were enhanced evidently, which was proved by dynamic contact angle analysis (DCAA), the contact angle in water of the fibers treated by air-DBD plasma decreased from 77.52° to 34.05°, while the surface free energy increased from 44.73 mJ/m² to 64.04 mJ/m². The surface morphology changes and variations of chemical components of PBO fibers were detected by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that the fiber surface morphology became rougher and some newly polar groups were introduced onto the fiber surfaces. They contributed to the enhancement of the wettability. Furthermore, the interfacial adhesion between PBO fibers and bismaleimide (BMI) resin was improved obviously, which revealed by the increased ILSS of the PBO/BMI composites. Nevertheless, the ILSS of PBO/BMI composites decreased to 47.0 MPa after PBO fibers were stored in air for 7 days and there were little changes for 7–30 days.     

Adhesion of PBO fiber in epoxy composites

A composite of poly p-phenylene-2,6-benzobisoxazole (PBO) fiber and epoxy resin has excellent electrical insulation properties. However, it is a challenging issue to improve its mechanical properties because of poor adhesion between PBO fiber and matrix. The relatively smooth and chemically inactive surface of PBO fiber prevent efficient chemical bonding in the composite interface. Here, we report the surface modification of PBO fibers by UV irradiation, O₂ and NH₃ plasma, as well as acidic treatments. We found that the surface free energy and roughness are increased for both sized and extracted fibers after plasma treatments together with maleic anhydride grafting. The sized fiber shows marginal improvement in adhesion strength and no change in fiber tensile strength because of the barrier effect of the finish. For the extracted fiber, however, the tensile strength of the fiber is sensitive to surface treatment conditions and considerable strength reduction occurred, particularly for cases of acidic treatments and UV irradiation. This is because that the treatments increase the surface roughness and introduce more surface flaws. The extracted fiber surface has no adequate wetting and functional groups, which in turn results in coarse interface structures and causes reduction or no apparent variation of the adhesion strength. The fracture surfaces after single fiber pull-out tests exhibit adhesive interfacial failure along the fiber surface, which is further confirmed by similar adhesion strength and interlaminar shear strength values when the fiber was embedded in various epoxy resins with different temperature behavior.     

离子基团对PBO 纤维的表面性能及其界面粘结性能的影响

PBO 作为增强纤维存在与环氧树脂基体界面粘结性能差的问题。通过在聚合过程中添加少量5-磺酸钠2间苯二甲酸部分替代对苯二甲酸与4 , 6-二氨基间苯二酚盐酸盐进行共聚, 合成了大分子链上含有离子基团的SPBO 共聚物, 并制得SPBO 初生纤维。通过接触角测试和XPS 研究了纤维的表面性能, 通过微脱粘实验和SEM评价了纤维与环氧树脂基体的界面粘结性能。结果表明: 与PBO 纤维相比, SPBO 纤维表面浸润性能提高, 表面含氮、氧量均增加, 与环氧树脂的界面剪切强度从8. 2 MPa 提高到10. 1 MPa , 提高了23 %。      

Effect of oxygen plasma treatment of PPTA and PBO fibers on the interfacial properties of single fiber/epoxy composites studied by Raman spectroscopy

The interfacial micromechanics of single poly(p-phenylene terephthalamide (PPTA) and poly(p-phenylene benzobisoxazole (PBO) fibers embedded in an epoxy resin has been investigated by determining the interfacial shear stress distributions along the fiber length. The effects of an oxygen plasma treatment on the interfacial shear stress of the fiber-epoxy systems are analyzed. Raman spectroscopy was used to map the stress distributions along the fiber when the composite is subjected to a small axial tensile strain (3.5% for PPTA and 2.5% for PBO). The quality of the interface or adhesion was improved after the surface treatment, supporting the ability of plasma oxidation to enhance the adhesion of high-performance fibers to epoxy resins. The tensile behavior of fiber-reinforced systems was different in each case. PPTA reinforcements underwent fragmentation, likely by fiber microfailure, whereas debonding or bridging is the most probable fragmentation mechanism in the case of PBO.     

高相对分子质量PBO的聚合及其高性能纤维的成型

以自行合成的4,6-二氨基间苯二酚盐酸盐（DAR）和商品对苯二甲酸（TPA）为单体原料,以多聚磷酸（PPA）为溶剂,制备了高相对分子质量PBO聚合物．研究了PBO聚合过程中TPA单体的粒径、溶剂的浓度以及搅拌器、聚合前脱除HCl的方式对PBO聚合和所得产物分子质量的影响．结果表明,TPA粒径小、聚合结束时PPA中P2O5的浓度维持在84％左右,有利于得到高相对分子质量的PBO聚合物．新型双螺带搅拌器能提高搅拌的效果,加压脱除HCl的工艺能有效地实旌聚合的稳定控制,利用双螺杆挤出机同时完成了后聚合和液晶纺丝,得到了特性粘度（｜η｜）达到20-30dL／g的PB0聚合物,采用干喷湿法成型制备出的金黄色的PB0纤维手感柔软、拉伸强度达到4．38GPa．     

Hydroxyapatite nanorod-reinforced biodegradable poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) composites for bone plate applications

Novel PLLA composite fibers containing hydroxyapatite (HAp) nanorods with or without surface lactic acid grafting were produced by extrusion for use as reinforcements in PLLA-based bone plates. Fibers containing 0–50% (w/w) HAp nanorods, aligned parallel to fiber axis, were extruded. Lactic acid surface grafting of HAp nanorods (lacHAp) improved the tensile properties of composites fibers better than the non-grafted ones (nHAp). Best tensile modulus values of 2.59, 2.49, and 4.12 GPa were obtained for loadings (w/w) with 30% lacHAp, 10% nHAp, and 50% amorphous HAp nanoparticles, respectively. Bone plates reinforced with parallel rows of these composite fibers were molded by melt pressing. The best compressive properties for plates were obtained with nHAp reinforcement (1.31 GPa Young’s Modulus, 110.3 MPa compressive strength). In vitro testing with osteoblasts showed good cellular attachment and spreading on composite fibers. In situ degradation tests revealed faster degradation rates with increasing HAp content. To our knowledge, this is the first study containing calcium phosphate–polymer nanocomposite fibers for reinforcement of a biodegradable bone plate or other such implants and this biomimetic design was concluded to have potential for production of polymer-based biodegradable bone plates even for load bearing applications.     

Barrier/bonding layers on bismuth telluride (Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>) for high temperature thermoelectric modules

In this research, a fundamental study is conducted to identify the materials and develop the processes for producing barrier/bonding composite on Bi₂Te₃ for high temperature thermoelectric applications. The composite must meet four basic requirements: (a) prevent inter-diffusion between the electrode material, for our design, silver(Ag) and Bi₂Te₃, (b) bond well to Bi₂Te₃, (c) bond well to Ag electrode, and (d) do not themselves diffuse into Bi₂Te₃. The composites investigated include palladium (Pd), nickel/gold (Ni/Au), Ag, and titanium/gold (Ti/Au). After annealing at 250 °C for 200 h, only the Ti/Au design meets all four requirements. The thickness of Ti and Au, respectively, is only 100 nm. Other than meeting these four requirements, the Ti/Au layers exhibit excellent step coverage on the rough Bi₂Te₃ surface even after the annealing process.     

MWNTs/PBO共混纤维的制备及性能

通过原位分散方法将不同含量的多壁碳纳米管（MWNTs）引入聚对苯撑苯并二噁唑（PBO）聚合体系,共混产物采用液晶纺丝法纺制成高性能MWNTs/PBO纤维。用偏光显微镜观察了MWNTs的分散状况,发现将MWNTs先预分散在多聚磷酸（PPA）中再添加可以有效地改善其分散性,热失重分析仪、强力仪研究了纤维的热稳定性能和力学性能。结果表明,MWNTs质量分数为2%的共混纤维的拉伸强度和模量分别达到4.69 GPa和128.8 GPa,比相同卷绕速度下PBO纤维提高了24.2%和23.5%,起始热分解温度也从668.9℃提高到700.8℃。MWNTs的质量分数达到5%时由于团聚严重,降低了PBO的可纺性,影响了纤维的性能。      

Stable Na Plating and Stripping Electrochemistry Promoted by In Situ Construction of an Alloy‐Based Sodiophilic Interphase

Sodium metal anodes are poor due to the reversibility of Na plating/stripping, which hinders their practical applications. A strategy to form a sodiophilic Au–Na alloy interphase on a Cu current collector, involving a sputtered Au thin layer, is shown to enable efficient Na plating/stripping for a certain period of time. Herein, electrochemical behaviors of Na plating on different substrates are explored, and it is revealed that the sodiophilic interphase can be achieved universally by in situ formation of M–Na (M = Au, Sn, and Sb) alloys during Na plating prior to Na bulk deposition in the initial cycle. Moreover, it is found that repetitive alloying–dealloying leads to falling‐off of thin film sodiophilic materials and thus limits the lifespan of efficient Na cycling. Therefore, an approach is further developed by employing particles of sodiophilic materials combined with the control over the cutoff potential, which significantly improves the stability of Na plating/stripping process. Especially, the low‐cost Cu@Sn‐NPs and Cu@Sb‐MPs composite current collectors allow Na plating and stripping to cycle for 2000 and 1700 times with the average efficiency of 99.9% at 2 mA cm^?2.     

电子封装用Diamond/Cu复合材料的化学镀镍

通过采用在Diamond/Cu复合材料表面化学镀镍的方法来改善其焊接性.化学镀镍前,采用SnCl2溶液和PdCl2溶液对复合材料表面进行敏化、活化等预处理.研究了pH值和温度对化学镀镍沉积速度的影响.利用SEM、EDX、XRD和划痕实验等措施对镀层进行了研究,结果表明,在Diamond/Cu复合材料表面获得了均匀、致密...     

Microscopic and macroscopic models of photo-induced volume changes in amorphous selenium

Electroless copper plating of polyester fabrics was demonstrated in the present investigation. The electroless Cu plating process on polyester fabric was modified by replacing the conventional PdCl₂ activator with an AgNO₃ activator to reduce the overall cost of the plating process. Both uncoated and Cu-coated polyester fabrics were characterized by the scanning electron microscope (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscope (XPS). Relatively uniform and continuous plating was obtained under the given plating conditions. The possible mechanism of electroless copper plating of polyester fabrics utilizing an AgNO₃ activator was suggested. The electromagnetic interference (EMI) shielding effectiveness (SE) was also evaluated to study the shielding behavior of copper-plated polyester fabrics. The results demonstrated that copper-plated polyester fabrics can be applied for EMI shielding.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

Preparation and Research of Electroless Copper on Carbon Fibers

In this paper, Cu coated carbon fibers were prepared using the electroless plating method. Effects of pretreatment, dispersing capability, formaldehyde, temperature, and pH on electroless plating process were studied. The connection between the Cu²⁺ concentration in the electroless plating solution and the plating time at different temperatures was studied. The process of the electroless Cu plating was analyzed and calculated, which derived the activation energy of the electroless copper plating on carbon fibers: Ea = 32.68 kJ/mol. The effect of the mass of carbon fibers and Cu coated carbon fibers which were dispersed in 80 mL distilled water on the conductivity of the solution was also studied. And as a result, the conductivity of the solution increased with the amount increasing. However, when the amount of the fibers was more than 0.08 g, the fibers would be incompletely dispersed. Thus, it could be concluded that the best accession amount of carbon fibers in 80 mL distilled water was 0.08 g. The corresponding conductivity values of carbon fibers and copper-coated fibers were 12.5 and 20.5 µs/cm, respectively.     

Young's modulus of electroplated Ni thin film for MEMS applications

The Young's modulus of an electroplated nickel (Ni) thin film suitable for microelectromechanical applications has been investigated as a function of process variables: the plating temperature and current density. It was found that the Young's modulus is approximately 205 GPa at plating temperatures less than 60 °C, close to that of bulk Ni, but drastically drops to approximately 100 GPa at 80 °C. The inclusion of ammonium and sulphate ions by hydrolysis is believed to be responsible for the sharp drop. The Young's modulus of 205 GPa is for a Ni film plated at J=2 mA/cm² and it decreases to 85 GPa as the plating current density is increased to 30 mA/cm². The results imply that at low current density, the plating speed is slow and there is sufficient time for the as-plated Ni atoms to rearrange to form a dense coating. At high currents, the plating speed is high, and the limited mass transport of Ni ions leads to a less dense coating.     

Tensile properties of elephant grass fiber reinforced polyester composites

Elephant grass stalk fibers were extracted using retting and chemical (NaOH) extraction processes. These fibers were treated with KMnO₄ solution to improve adhesion with matrix. The resulting fibers were incorporated in a polyester matrix and the tensile properties of fiber and composite were determined. The fibers extracted by retting process have a tensile strength of 185 MPa, modulus of 7.4 GPa and an effective density of 817.53 kg/m³. The tensile strength and modulus of chemically extracted elephant grass fibers have increased by 58 and 41%, respectively. After the treatment the tensile strength and modulus of the fiber extracted by retting have decreased by 19, 12% and those of chemically extracted fiber have decreased by 19 and 16%, respectively. The composites were formulated up to a maximum of 31% volume of fiber resulting in a tensile strength of 80.55 MPa and tensile modulus of 1.52 GPa for elephant grass fibers extracted by retting. The tensile strength and the modulus of chemically extracted elephant grass fiber composites have increased by approximately 1.45 times to those of elephant grass fiber composite extracted by retting. The tensile strength of treated fiber composites has decreased and the tensile modulus has shown a mixed trend for the fibers extracted by both the processes. Quantitative results from this study will be useful for further and more accurate design of elephant grass fiber reinforced composite materials.