The effects of nitrogenation on the electrochemical properties of nanocrystalline diamond films

The effect of the nitrogenation on the electrochemical properties of nanocrystalline diamond films produced by microwave plasma CVD in CH₄–Ar–H₂–N₂ gas mixtures was studied systematically, using cyclic voltammetry and electrochemical impedance spectroscopy measurements, for the first time. Differential capacitance, kinetic parameters of reactions in [Fe(CN)₆]^3-/4-redox system and potential window were found to be sensitive to the nitrogen concentration in the process gas. With its increase (from 0 to 25%), a transition of the NCD film behavior from “poor conductor” to metal-like character takes place. The heavily N-doped nanocrystalline diamond films have satisfactory electrochemical properties to be used as electrodes.     

Influence of curing temperature on properties of the polyacrylonitrile/polyimide composite films

A series of polyacrylonitrile/polyimide (PAN/PI) composite films with different PAN contents are prepared under given curing temperatures (250, 300, 350, and 400°C). The microstructure of the composite films is observed by SEM, and the thermal, dielectric and mechanical properties of the composite films are determined. The results show that the self‐assembly behavior of polyamic acid gives rise to connected network structure in the composite films and the variations in the microstructure of the composite films cured at different temperatures show important effects on the properties of PAN/PI composite films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40283.     

硫化体系对丁腈橡胶高温力学性能的影响

研究了不同硫化体系对丁腈橡胶硫化胶在不同温度下力学性能的影响。结果表明,不同硫化体系硫化丁腈橡胶的拉伸强度和撕裂强度都随温度的升高而逐渐降低,且降低趋势有所减弱。4种硫化胶中,DCP硫化体系的硫化胶具有最好的高温拉伸强度和最差的高温撕裂强度;测试温度低于75℃时,CV硫化体系硫化胶的撕裂强度最好,SEV硫化体系的硫化胶稍差;测试温度超过75℃后,SEV硫化体系硫化胶的撕裂强度最好。丁腈橡胶硫化胶的常温和高温拉伸断面形态明显不同,常温断面的炭黑颗粒大部分被包覆在橡胶基质中,断面比较光滑;高温断面的炭黑颗粒则大部分半裸露或全裸露出橡胶基质,断面比较粗糙。     

Low surface energy films based on partially fluorinated isocyanates: the effects of curing temperature

Self-stratification strategy can be used to prepare films in which both bulk and surface properties can be optimized. By using this approach, only a very small quantity of fluorinated species is needed to generate a surface with low surface energy. When cross-linking is involved during film formation, we are dealing with a competition behavior between the diffusion of fluorinated species and the formation of cross-linked network. In this study low surface energy polymeric films were prepared on the basis of partially fluorinated polyisocyanates, in combination with hydroxyl-end-capped three-armed solventless liquid oligoesters and modified hyperbranched polyesters. At a fluorine concentration of only 0.5 wt.%, contact angles of water and hexadecane can reach 120° and 80°, respectively. A surface energy as low as 10–15 mN/m can be obtained upon the addition of less than 1 wt.% of fluorine in the films. It was shown, from real time ATR-FTIR and contact angle measurements, that the curing temperatures demonstrated significant effects on the cross-linking rate as well as on the wettability of the films.     

The effects of additives on curing properties,resin contents,and mechanical properties of graphite/epoxy composites

The effects of additives such as boron trifluride-monoethylene amine (BF₃MEA) and fumed silica in the TGDDM/DDS epoxy formulations on the curing properties, resin contents, and mechanical properties of their graphite/epoxy (Gr/Ep) composites were investigated. The addition of BF₃MEA increased the viscosity of resin as well as the resin contents of cured laminates because of its catalytic effect. Although the fumed silica was considered a thickening agent, it also acted like a co-catalyst with BF₃MEA. As the resin content of cured laminates was increased, the excess resin was likely to accumulate in the interlaminar region, which increased the interlaminar shear strength but decreased the flexure strength as well as the interlaminar fracture toughness value, G_IC.     

脲醛树脂/淀粉复合体系的常温固化及其力学性能

在脲醛树脂(UF)/淀粉(St)复合体系中引入聚醋酸乙烯酯(PVAc)、聚丙烯酰胺(PAM),氨基硅烷偶联剂(A212),通过力学性能测试和扫描电镜分析研究了复合体系的常温固化过程、材料微观结构及其性能变化的关系。结果表明,当m(UF)/m(St)/m(PVAc)/m(固化剂CA)/m(PAM)/m(A212)=200/50/2/3/5/0.06时,体系冲击强度为190kJ/m2,弯曲强度为24MPa。PVAc的引入延长了体系的固化时间,PAM较好地改善了体系的分散状态。A212明显改善了体系分散的均匀性和相界面结合状态,材料微观结构更为致密,力学性能提高,尤其是韧性明显改善。     

UV exposure and temperature effects on curing mechanisms in thin linseed oil films: Spectroscopic and chromatographic studies

The influence of thermal and photochemical treatment in the curing mechanisms of thin linseed oil films is studied. The role of copper acetate pigments is also investigated under the above conditions. UV and FTIR absorption spectroscopy and chromatographic product analysis are used as the main analytical techniques, which allowed the identification of significant changes in the curing mechanism in each case. Yellowing, crosslinking, and fragmentation inside the film material proceed to a different extent according to the conditions. Peroxide destruction is induced by UV exposure at early curing stages and affects the course of the yellowing process. Yellow product formation is also favored by curing at elevated temperatures, which is accompanied in this case by decreased crosslinking in the cured film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 936–949, 2002; DOI 10.1002/app.10117     

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films were extensively investigated by means of several series of model latexes with varying backbone polymer crosslinking density and interfacial crosslinking functional groups. It was found that the tensile strength of crosslinked model latex films increased with increasing gel content (i.e. crosslinking density) of latex backbone polymers up to about 75% and then decreased with further increase in gel, while their elongation at break steadily decreased with increasing gel content. These findings showed that latex particle coalescence was retarded above a gel content of about 75% so that the limited coalescence of latex particles containing gel contents higher than 75% prevented the tensile strength of crosslinked latex films from increasing by further crosslinking the latex backbone polymers. This was contrary to the theory of rubber elasticity that the tensile strength increases with increasing molecular weight and crosslinking density. This limitation was found to be overcome by the interfacial crosslinking among latex particles during film formation and curing. This paper will discuss the effects of both latex backbone polymer and interfacial crosslinking on latex film properties. It will also discuss the development of self-curable latex blends and structured latexes containing co-reactive groups: oxazoline and carboxylic groups.     

Annealing effects on the mechanical properties of near-frictionless carbon thin films

In this work, the near-frictionless carbon (NFC) thin films developed at Argonne National Laboratory were annealed at 100 °C, 150 °C, 200 °C, 400 °C, and 600 °C in nitrogen atmosphere. The changes of the NFC mechanical properties were measured with both static and dynamic nanoindentation methods. It was found that the Young's modulus and hardness decreased with increasing annealing temperatures. Raman spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the film's structural change before nanoindentation testing. Raman characterization indicated that the G peak shifted upwards as the annealing temperature was increased above 150 °C, which indicated decreasing sp³ content. The intensity of the D peak was shown to increase with annealing temperature indicating that the NFC film became more graphite-like. AFM analysis showed an increase of sp² clustering with annealing temperature, which resulted in an increase in surface roughness. SEM characterization indicated that as the films were annealed large cracks and numerous pinholes were generated. The characterization results were in good agreement with the measured mechanical properties.     

Structural and electrical properties of the sol-gel derived multiferroic BiFeO3 monolayer and NiTiO3-BiFeO3 bilayer thin films

In this paper, the multiferroic BeFiO₃ monolayer and NiTiO₃–BiFeO₃ bilayer thin films were fabricated by spin-coating method on the SrRuO₃/n⁺-Si substrate. The structural and ferroelectric properties of multiferroic BeFiO₃ monolayer and NiTiO₃–BiFeO₃ bilayer thin films were investigated. Both multiferroic films showed the typical XRD patterns of the perovskite structure without presence of the second phase. The electrical properties, such as leakage current and remnant polarization, of the NiTiO₃–BiFeO₃ bilayer film were superior to those of BeFiO₃ monolayer film, which those values were 1.94 × 10⁻⁴ A/cm² at electric field of 0.75 MV/cm and 14.05 μC/cm², respectively. This outcome is due to the NiTiO₃–BiFeO₃ bilayer film with a high Schottky barrier height as well as a top NiTiO₃ layer on the BiFeO₃ film inducing the strain-induced polarization rotation and forming the strong domain-wall pinning.     

Dopant effects on high temperature mechanical properties of zirconium carbide ceramics

Combining theoretical and experimental methods, the effects of 5?vol.-% WC dopant on the microstructure evolution, sintering behaviour and mechanical properties of ZrC ceramics were investigated. WC dopant was found to improve the high temperature elastic modulus and bending strength of ZrC ceramics. Both calculations and experimental results showed that the formation of (Zr, W)C solid solution promote dissolution of the impurity oxygen from the starting powder into the lattice sites, resulting in less oxygen defects in grain boundaries. Internal friction curve can also conform that the ZrC ceramics doped with WC have cleaner grain boundaries, which improved higher elastic modulus and bending strength in WC doped ZrC ceramics at elevated temperature.     

AZO基双层/多层薄膜的制备及性能

采用磁控溅射法在普通钠钙浮法玻璃表面先获得厚度为50 nm的AZO(掺铝氧化锌)底层,然后制备出不同Ag层厚度(4、6、8或10 nm)的Ag/AZO双层膜以及不同AZO顶层厚度(10、30、50或70 nm)的AZO/Ag/AZO多层膜,考察了它们的表面形貌、晶体结构、方块电阻、透光率和品质因子.结果表明,Ag层厚度为6 nm时,Ag/AZO双层膜表面Ag粒子分布均匀,致密度较好,晶粒尺寸最大,综合性能最佳.在此双层膜的基础上沉积50 nm厚的AZO顶层可以较好地覆盖Ag层,提高薄膜的致密度,令晶粒尺寸明显增大,得到综合性能最佳的AZO/Ag/AZO多层膜.     

Study on morphology control and how to affect mechanical properties of polyimide/silica hybrid films

A series of polyimide (PI)/silica hybrid films were prepared by sol–gel method, using hydrolyzed tetraethoxysilane and poly amic acid‐imides (PAA‐Is), which were different imidization degree controlled by chemical imidization method. The imidization degree was characterized by Fourier transform infrared spectra and their corresponding morphology was characterized by scanning electron microscopy. The results show that there are two kinds of silica particles and their formative morphology obeys the double phase separation mechanism. According to the increase of PAA‐I imidization degree, amount of nano silica particles decreased and the diameter of macro silica particles increased in the hybrid films. Tensile testing, dynamic mechanical analysis, and thermal mechanical analysis results show that, according to the amount of nano silica particles increasing, the hybrids have the higher the mechanical properties, glass transition temperature (T_g), and thermal expansion coefficient. Through controlling PI/silica hybrid films microstructure, its mechanical properties can be controlled. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The preparation of hybrid films of carbon nanotubes and nano-graphite/graphene with excellent mechanical and electrical properties

We have prepared mixed dispersions of singlewalled nanotubes and nano-graphite/graphene in the solvent N-methyl pyrrolidone. This allows the deposition of hybrid films by vacuum filtration. Scanning electron microscopy shows the components to be well mixed with little sign of phase separation. Although dominated by nano-graphite, Raman spectroscopy shows the presence of some graphene flakes with <5 layers. Mechanical measurements show the hybrids to be stronger and stiffer than nanotube or graphene-only films, reaching strengths and stiffnesses of 38 MPa and 4.8 GPa, respectively for the sample with 20 wt% graphene. In addition the hybrid films were more electrically conductive than the nanotube-only or graphitic films reaching a DC conductivity of 2 × 10⁴ S/m for the 70 wt% nano-graphite/graphene sample.     

Time and temperature effects on the ultimate properties of thermally oxidized polypropylene films

The ultimate properties of thermally oxidized polypropylene (PP) films have been determined. Attention was focused on the variation of draw stress, tensile strength, draw ratio, breaking extension, breaking factor, work of draw, and work of rupture, with a change in temperature and time of heat treatment. While the draw stress and draw ratio increased with increase in temperature, the tensile strength, breaking extension, work of rupture, and work of draw decreased with increase in temperature. The breaking factor, rather, attained a maximum at 110°C before decreasing with further increases in temperature. The PP films thermally oxidized at 60°C exhibited larger values for the following properties: tensile strength, breaking extension, draw ratio, work of rupture, work of draw, and breaking factor, than for the 100°C oxidized PP films. While breaking extension and tensile strength just decreased with increasing the log time (min), the draw stress, draw ratio, work of rupture, and work of draw were linear functions with negative slopes of log time (min) of thermal oxidation at a particular temperature. The decrease in all properties studied were explained by decrease in the density of aged PP films. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1217–1226, 1997     

The effects of polyamic acid on curing behavior,thermal stability,and mechanical properties of epoxy/DDS system

A thermoplastic modification method was studied for the purpose of improving the toughness and heat resistance and decreasing the curing temperature of the cured epoxy/4, 4′‐diaminodiphenyl sulfone resin system. A polyimide precursor‐polyamic acid (PAA) was used as the modifier which can react with epoxy. The effects of PAA on curing temperature, thermal stability and mechanical properties were investigated. The initial curing temperature (T_i) of the resin with 5 wt % PAA decreased about 50°C. The onset temperature of thermal decomposition and 10 wt %‐weight‐loss temperature for the resin system containing 2 wt % PAA increased about 60°C and 15°C respectively. Besides, the value of impact toughness and plain strain fracture toughness for the modified epoxy resin increased ～ 190% and 55%, respectively. Those changes were attributed to the outstanding thermal and mechanical properties of polyimide, and more importantly to formation of semi‐interpenetrating polymer networks composed by the epoxy network and linear PAA. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Alginate and carboxymethyl cellulose in monolayer and bilayer films as wound dressings: Effect of the polymer ratio

In this study, we investigated different proportions of alginate and carboxymethyl cellulose (CMC) biopolymers in the formulation of films to act as wound dressings. With the casting method, monolayer and bilayer (BL) films were produced with alginate/CMC proportions (weight percentages) of 0:100 (0A), 25:75 (25A), 50:50 (50A), 75:25 (75A), and 100:0 (100A). Thin, homogeneous, and continuous films were obtained with glycerol and crosslinking with CaCl₂. The fluid uptake, film stability, and morphological, mechanical, thermal, and barrier properties were evaluated. A general tendency of the film characteristics was visualized: 50A had intermediary characteristics from both polymers; although the liquid behavior characteristics were improved with increasing CMC content, the mechanical properties worsened. When compared to the monolayer film (50A), the BL film 50A–BL demonstrated a better water vapor transmission rate. In this study, we demonstrated the necessity of varying the polymer concentrations to assist in the production of wound dressings. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46941.     

机械弹性车轮硫化预热温度研究

对机械弹性车轮硫化前预热温度进行研究。通过建立车轮硫化模型,使用Ansys软件对机械弹性车轮硫化过程进行热力学仿真,分析对比了不同预热温度对车轮硫化温升过程和硫化程度的影响。结果表明:预热温度对车轮不同部位硫化温升过程的影响存在差异,距离外部热源越远的部位受预热温度的影响越大,车轮过硫率随着预热温度的升高呈上升趋势,车轮的硫化一致性则呈明显的下降趋势。     

The effect of curing additive on the mechanical properties of phthalonitrile-carbon fiber composites

Unidirectional carbon fiber-reinforced phthalonitrile composite panels were fabricated by prepreg consolidation with bis[4-(4-aminophenoxy)phenyl]sulfone (p-BAPS) as the phthalonitrile curing additive. Rheometric measurements and elevated-temperature, short beam shear tests were used to evaluate the cure of the composite as a function of the cure and postcure conditions. These techniques revealed that a fully cured phthalonitrile composite was obtained when the composite was heated at 375°C for 8 hours. Room-temperature mechanical properties of the cured composite were then evaluated using short beam shear, tension, and flexural tests. The results are compared with those obtained by curing the phthalonitrile with 1,3-bis(3-aminophenoxy)benzene (m-APB). The data indicate that substitution of p-BAPS for m-APB has little effect on the mechanical properties of the cured composite. Elevated-temperature, short beam shear studies up to 371°C show that the cured phthalonitrile composite retains approximately 70% of its room-temperature apparent interlaminar shear strength. The composite also retains 70% of its room-temperature storage modulus up to 450°C. Polym. Compos. 25:554–561, 2004. © 2004 Society of Plastics Engineers.     

Substrate effects on the mechanical properties and contact damage of diamond-like carbon thin films

Substrate effects on the mechanical properties and contact damage of diamond-like carbon (DLC) films have been investigated. To that end, a DLC film of 1 μm thickness was deposited on two different substrates: soda–lime glass (compliant and soft), and single-crystal silicon (stiff and hard). The elastic modulus and hardness were measured by means of nanoindentation. Quasi-static and sliding contact configurations were simulated by means of ultra-micro indentation, and surface and cross-sectional damage were assessed using a focused ion beam (FIB) miller. It was found that a compliant and soft substrate enhances crack initiation on the film surface in the form of ring/cone cracks. On the other hand, a stiff and hard substrate delays crack initiation in the film, but is more susceptible to fracture in the form of median and lateral cracks due to increased brittleness. The results have implications for the reliability of DLC-coated systems.