Effects of plasma surface modification on the mechanical properties of carbon fiber and carbon fiber/epoxy composite

_The effect of surface treatment on mechanical properties of carbon fibers has been investigated by application of plasma polymerization of selected monomers in the vapor phase. The role of the fiber-matrix interface on carbon fiber-reinforced epoxy resin composites has also been studied. Composites have been prepared separately by the use of plasma-modified and unmodified carbon fibers in the epoxy resin matrix. The mechanical properties of carbon fibers (Hercules and Grafil) as well as of fiber/epoxy composites were examined by using single filament and three-point bending tests, respectively. It was observed that plasma polymerization treatment at selected plasma conditions led to significant improvement of interlaminar shear and flexural strength values of composites.     

Surface modification and submicron structure of carbon fibers through high current pulse

This paper investigated the behavior of carbon fibers subjected to a ∼20 kA, ∼5 μs high current pulse. It was found that the broken fibers and submicron particles were generated by electrical explosion process. After high current pulsed discharge, the fiber diameter increased significantly, from 5-7 μm to ∼13 μm. Also, the surface rupture of carbon fibers with valleys of hundreds of nanometers was observed. Most notably, the submicron particles appeared with two typical shapes (near-sphere and square). The high current pulsed discharge of carbon fibers can be divided into three stages, namely, heating stage, phase change stage, and explosion stage. Indeed, the electrical explosion process occurred in the last stage of ∼200 ns. The nature behind these results is closely related to the plasma development during the explosion process. The plasma expansion due to a large plasma thermal stress leads to the incomplete explosion. In the explosion stage, the current passing through the fibers exhibited a huge fluctuation, indicating plasma instabilities. Finally, the physical mechanisms, how to affect the surface morphology of carbon fibers, are presented.     

Surface modification of polyacrylonitrile-based carbon fiber and its interaction with imide

In this work, sized polyacrylonitrile (PAN)-based carbon fibers were chemically modified with nitric acid and maleic anhydride (MA) in order to improve the interaction between carbon fiber surface and polyimide matrix. Bismaleimide (BMI) was selected as a model compound of polyimide to react with modified carbon fiber. The surface characteristic changing after modification and surface reaction was investigated by element analysis (EA), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and surface enhanced Raman scattering (SERS). The results indicated that the modification of carbon fiber surface with MA might follow the Diels Alder reaction mechanism. In the surface reaction between modified fibers and BMI, among the various surface functional groups, the hydroxyl group provided from phenolic hydroxyl group and bridged structure on carbon fiber may be the most effective group reacted with imide structure. The results may shed some light on the design of the appropriate surface structure, which could react with polyimide, and the manufacture of the carbon fiber-reinforced polyimide matrix composites.     

Role of curing conditions and silanization of glass fibers on carbon nanotubes (CNTs) reinforced glass fiber epoxy composites

Curing behavior of amino-functionalized carbon nanotubes (ACNT) used as reinforcing agent in epoxy resin has been examined by thermal analysis. Experiments performed as per supplier’s curing conditions showed that modification of the curing schedule influences the thermo-mechanical properties of the nanocomposites. Specifically, the glass transition temperature (T_g) of ACNT-reinforced composites increased likely due to the immobility of polymer molecules, held strongly by amino carbon nanotubes. Further, a set of composites were prepared by implementing the experimentally determined optimal curing schedule to examine its effect on the mechanical properties of different GFRP compositions, while focusing primarily on reinforced ACNT and pristine nanotube (PCNT) matrix with silane-treated glass fibers. From the silane treatment of glass fibers in ACNT matrix composition it has been observed that amino silane is much better amongst all the mechanical (tensile and flexural) properties studied. This is because of strong interface between amino silane-treated glass fibers and modified epoxy resin containing uniformly dispersed amino-CNTs. On the other hand, PCNT GFRP composites with epoxy silanes demonstrated enhanced results for the mechanical properties under investigation which may be attributed to the presence of strong covalent bonding between epoxy silane of glass fiber and epoxy–amine matrix.     

Surface Analysis of PBO and Modified SPBO Fiber by Contact Angle Measurements and XPS

In order to improve surface properties of poly (p‐phenylene benzoxazole) (PBO) fiber, modified SPBO containing ionic groups (–NaSO₃) was prepared for the first time by polymerization from 1, 3‐diamino‐4, 6‐dihydroxybenzene dihydrochloride (DAR) and terephthalic acid (TPA), with addition of selected amounts of 5‐sulfoisophthalic acid monosodium salt (SIPA) in place of the TPA. The SPBO polymer with a different content of SIPA, 1.5% SPBO (mol ratio), and 3% SPBO was prepared. The SPBO fiber was obtained via liquid crystal spinning through dry‐jet wet‐spinning techniques. The contact angles between fiber and water/ethyl alcohol were measured by an OCA 40 Micro dynamic contact angle analysis system. The contact angles of SPBO to water and alcohol were smaller than those of PBO to either of them and the wetting process of water and ethyl alcohol on SPBO fiber was faster than on PBO fiber. In addition, the results showed that the surface free energy could be increased up to 40.3 mJ/m², i.e. by 13.55%. Through XPS analysis, it was found that the surface nitrogen‐to‐carbon ratio was increased from 0.0157 to 0.0915 and the oxygen‐to‐carbon ratio was increased from 0.2331 to 0.3070 after incorporation of the ‐NaSO₃ ionic groups; in addition, the ionization energy (or binding energy) of C_1s and O_1s decreased.     

Polarization behaviors of twisted carbon nanotube fibers

Polarization behaviors of carbon nanotube (CNT) fibers with different twisting were reported. Scanning electron microscope and polarized Raman spectroscopy were used to investigate the prepared samples. Results indicate that surface twisting angle affects greatly the polarization angle and I_///I_⊥ ratio of twisted CNT fibers. Raman depth profile measurements imply that the twisted fibers consist of non‐uniform CNT alignments. A simplified two‐CNT‐alignment geometric model was proposed to illuminate the experimental observations. The results suggest that polarized Raman depth profile measurement would be a very useful approach for determining the distribution of CNT alignments in CNT fibers. Copyright © 2012 John Wiley & Sons, Ltd.     

Surface characterization of electrochemically oxidized carbon fibers: surface properties and interfacial adhesion

Carbon fibers are oxidized in two electrolytes at different electrolyte concentrations and potentials. The chemical composition of the fiber surface changes considerably in both cases. The oxidation in H₂SO₄ results in the formation of sulfur containing groups, but quinoidal compounds are also detected on the surface. The concentration of all functional groups increases with increasing electrolyte concentration at 5 V, but does not change as a function of oxidation potential in 20 wt% solutions below this value. Carboxylic functional groups are formed on the fiber in NaOH, but some adsorbed NaOH also remains on the surface after oxidation. Cyclic voltammetry reflects the modification of the surface differently. Peak potentials remain basically constant, while peak currents depend on the type of the treatment. Good correlation has been found among peak current, the chemical composition of the fiber surface and IFSS of epoxy composites in the case of H₂SO₄. The adsorbed NaOH interferes with the electrochemical reaction that takes place on the fiber surface. Moreover, IFSS decreases as the amount of adsorbed NaOH increases.     

Surface modification and characterization of magnesium hydroxide sulfate hydrate nanowhiskers

In order to enhance the compatibility with plastic polymers, magnesium hydroxide sulfate hydrate (MHSH) nanowhiskers were modified through grafting methyl methacrylate (MMA) on the surface of the nanowhiskers by emulsion polymerization. The influences of the reaction time, MMA monomer content, adding speed of monomer and the reaction temperature on the grafting ratio were investigated. Thermogravimetry (TG), Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray (EDX) spectroscopy and surface contact angle measurement were used to characterize the effect of surface modification. The results showed that the MHSH nanowhiskers were uniformly coated by polymethyl methacrylate (PMMA), and a well-defined core-shell hybrid structure of MHSH/PMMA was obtained. The surface contact angle of the hybrid whiskers increased to 87.32° from 12.71° and the whiskers surface was changed from hydrophilic to lipophilic.     

臭氧化法表面改性聚苯乙烯薄膜

为增强聚苯乙烯(PS)与聚乙烯醇(PVA)之间的结合力,进而提高PS-VA双层空心微球存活率。利用臭氧化改性法在酸性介质中对聚苯乙烯薄膜进行表面改性,用红外光谱对处理后的表面进行了半定量的分析。结果表明：改性过后聚苯乙烯表面产生羟基、羰基等极性基团;接触角测试证明,处理后的表面由憎水变为亲水,并通过纳米压痕划痕法得到了处理前后PS与PVA薄膜之间的相互作用强度,臭氧化改性后PS与PVA膜间作用强度增大了40%。     

Surface Modification of Para-Aramid Fiber by Direct Fluorination and its Effect on the Interface of Aramid/Epoxy Composites

Surface modification of a para-aramid fiber (DAFIII) was performed by direct fluorination. The properties of treated and untreated fibers were characterized and compared in detail by mechanical testing, Fourier transform infrared (FTIR) spectroscopy characterization, X-ray photoelectron spectroscopy (XPS) analysis and static contact angle measurements. The results showed that little damage of the fiber occurred after direct fluorine treatment, and the content of polar groups on the fibers surfaces were increased significantly, which resulted in a lower value of contact angle. The interlaminar shear strength (ILSS) of DAFIII fiber/epoxy composites and the tensile strength of NOL-ring specimens increased by 33% and 12%, increasing to 56.2 MPa and 2340 MPa, respectively, which indicated that the interfacial adhesion between the matrix and the aramid fiber was improved significantly by the fluorination treatment. Further tests showed that the durability of the direct fluorination treatment on the aramid fiber was also satisfactory.     

臭氧化法表面改性聚苯乙烯薄膜

 为增强聚苯乙烯(PS)与聚乙烯醇(PVA)之间的结合力,进而提高PS-VA双层空心微球存活率。利用臭氧化改性法在酸性介质中对聚苯乙烯薄膜进行表面改性,用红外光谱对处理后的表面进行了半定量的分析。结果表明：改性过后聚苯乙烯表面产生羟基、羰基等极性基团;接触角测试证明,处理后的表面由憎水变为亲水,并通过纳米压痕划痕法得到了处理前后PS与PVA薄膜之间的相互作用强度,臭氧化改性后PS与PVA膜间作用强度增大了40%。     

醇水混合冷却剂表面张力和接触角的测定

喷雾冷却具有散热能力强、冷却工质需求量小等优点,在解决电子器件散热方面具有广阔的应用前景。纯水中添加醇类可以有效提升喷雾冷却性能。为进一步探索醇类添加剂强化喷雾冷却性能的机理,本文开展醇水混合溶液表面张力和接触角的实验测定研究。分别在水中加入不同浓度的乙醇、正丙醇、正丁醇、正戊醇、正己醇、正庚醇和正辛醇等醇类,利用悬滴法探究醇类浓度对溶液的表面张力的影响规律;利用Young-Laplace坐滴法探究醇类浓度对接触角的影响规律。结果表明,水中添加醇类后表面张力降低,且其随醇类溶质浓度的增加而变小,且其下降速率均随浓度的增加越来越慢;添加低醇类添加剂均可降低溶液的接触角,而高醇类接触角随浓度变化没有明显的变化规律。     

Surface modification of magnetic nanoparticles in biomedicine

Progress in surface modification of magnetic nanoparticles(MNPs)is summarized with regard to organic molecules,macromolecules and inorganic materials.Many researchers are now devoted to synthesizing new types of multi-functional MNPs,which show great application potential in both diagnosis and treatment of disease.By employing an ever-greater variety of surface modification techniques,MNPs can satisfy more and more of the demands of medical practice in areas like magnetic resonance imaging(MRI),fluorescent marking,cell targeting,and drug delivery.     

壁面温度对疏水表面上水滴冻结的影响

本文研究了冷壁面温度对疏水表面(θ=108.8°)上单个水滴冻结过程的影响,比较了水滴的冻结时间及冻结前后的形态变化。结果表明,水滴冻结所需要的时间随冷表面温度的降低而减小,冷表面温度越低,水滴冻结后其顶端越容易出现树枝状霜晶生长。最后,根据能量守恒原理建立了冷表面上水滴冻结的数学模型,给出了相应的表达式,进而分析了壁面温度对水滴冻结时长的影响,计算结果与实验结果一致。     

Surface analysis of plasma grafted carbon fiber

The surface characteristics of carbon fibers were studied by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and wetting measurements. The surface of carbon fiber was modified by means of plasma graft silsesquioxane. The oxygen/carbon and silicon/carbon ratio increased rapidly after treatments. Fitting the C 1s, O 1s, and Si 2p spectra demonstrated that new photopeaks were emerged, which were indicated C-Si, Si-O groups, respectively. The degree of surface roughness and the wettability of carbon fiber surface were both increased by plasma graft silsesquioxane. The results may shed some light on the design of the appropriate surface structure, which could react with resin, and the manufacture of the carbon fiber reinforced composites.     

Surface modification of Angora rabbit fibers using dielectric barrier discharge

Dielectric barrier discharge (DBD) of Helium and Helium + air modify the surface of Angora rabbit fibers. DBD treatment carried out at different power densities, changes the morphology and chemical composition of the surface of Angora fiber. Scanning electron microscopy (SEM) results reveal that the DBD treatment eliminates fibrosity from the fiber surface. X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer (FTIR) spectrum confirm the increase in oxygen bonding at the surface. These changes reduce shedding of the fibers and improve dye-uptake property. However, even after 10 min of plasma exposure the thermal insulation (heat keeping ratio) of Angora fibers nearly remain unchanged. It has been noticed that DBD treatment (10 min) reduces whiteness of the fiber.     

Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

A study on UV laser drilling of PEEK reinforced with carbon fibers

This paper deals with the application of Nd-YAG laser emitting at 355 nm to the drilling process of Carbon Fiber Reinforced Polyetheretherkethone (PEEK-CF) laminates. The combination of a modern UV-laser source with a scanning technology enabling speeds up to 4 m/s, suppresses heat affected zones (HAZ) and consequently detachment of fibers from the polymer matrix. A removal technique based on the ablation of superimposed layers of composite material is proposed and analyzed in detail as a function of energy density delivered to the surface, hatch strategy and thickness of the laminate to be drilled. The hatching technique discussed in the paper is compared with conventional laser trepanning and percussion drilling through holes for the realization of 2 mm and 0.1 mm diameter, respectively. In both the cases benefits were noticed in terms of extension of HAZ and quality of the cut edges.     

Surface modification of diamond-like carbon films with perfluorooctyl functionalities and their surface properties

Photolysis of perfluoroazooctane with diamond-like carbon (DLC) films led to the surface modification to introduce perfluorooctyl functional groups, confirmed by means of FT-IR, XPS, Raman and TOF-SIMS measurements. The DLC films modified with fluorine moieties showed reduction of the surface energy evaluated by contact angle to water, as compared with pristine DLC film. The contact angle of chemically modified DLC film is 105°, comparable to that of polytetrafluoroethylene (PTFE). By monitoring with XPS, we found that the results on the value of fluorine/carbon ratio of fluorinated DLC films depending on irradiation time are consistent with those of contact angle. Chemical modification of DLC films with perfluorooctyl functionalities also led to improvement of their frictional properties. The friction coefficient of the modified film is 0.05 under vacuum condition, whereas that of the pristine film shows very high value (>1).     

Fabrication of protective tantalum carbide coatings on carbon fibers using a molten salt method

Protective tantalum carbide (TaC) coatings were fabricated successfully on carbon fibers in the temperature range of 950-1100 °C using a molten salt method. A salt mixture composed of LiCl-KCl-KF was used as a reaction medium in which the tantalum and the carbon fiber substrates reacted to form the TaC coatings. The structure and morphology of the TaC coatings were characterized by XRD, SEM and EDX analyses. The results show that the reaction temperature and time have significant influence on the thickness, integrity and surface morphology of the TaC coatings. A uniform, adherent and crack-free TaC coating can be obtained by controlling the reaction temperature and time. Thermo-gravimetric analysis indicated that the oxidation resistance of the carbon fibers was improved remarkably by coating them with a high-quality TaC layer.