航天材料的抗原子氧防护技术研究进展

在低地球轨道环境中,航天器表面材料受到侵蚀最为严重.介绍了原子氧对航天用材料的侵蚀情况,并且阐述了近些年来研究人员对原子氧侵蚀的多种防护措施及效果,包括涂层型抗原子氧侵蚀材料、本征型抗原子氧侵蚀材料、添加型抗原子氧侵蚀材料、界面自组装等.     

Studies on the surface free energy and surface structure of PTFE film treated with low temperature plasma

The surface free energy and surface structure of poly(tetrafluoroethylene) (PTFE) film treated with low temperature plasma in O₂, Ar, He, H₂, NH₃, and CH₄ gases are studied. The contact angles of the samples were measured, and the critical surface tension γ_c (Zisman) and γ_c (max) were determined on the basis of the Zisman's plots. Furthermore, the values of nonpolar dispersion force γ^a_s, dipole force γ^b_s, and hydrogen bonding force γ^c_s to the surface tensions for the plasma-treated samples were evaluated by the extended Fowkes equation. Mainly because of the contribution of polar force, the surface free energy and surface wettability of PTFE film which was treated with H₂, He, NH₃, Ar, and CH₄ for a short time increased greatly. Electron spectroscopy for chemical analysis (ESCA) shows that the reason was the decrease of fluorine and the increase of oxygen or nitrogen polar functional group on the surface of PTFE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1733–1739, 1997     

In situ atomic oxygen erosion study of fluoropolymer films using X‐ray photoelectron spectroscopy

The surfaces of a homologous series of fluoropolymers were characterized in situ using X‐ray photoelectron spectroscopy before and after a 15‐min exposure to the flux produced by a unique hyperthermal atomic oxygen (AO) source, which produces a flux of about of 10¹⁵ atoms cm^?2 s^?1. The linear polymers investigated in this study include high‐density polyethylene (HDPE), poly(vinyl fluoride) (PVF), poly(vinylidene fluoride) (PVdF), and poly(tetrafluoroethylene) (PTFE). They possess a similar base structure with increasing fluorine‐to‐carbon ratios of 0, 1 : 2, 1 : 1, and 2 : 1, respectively. No interaction of the AO with the nonfluorine‐containing linear polymer HDPE was detected over this short exposure. However, a correlation exists between the chemical composition of the fluorinated polymers and the induced chemical and structural alterations occurring in the near‐surface region as a result of exposure to AO. The data indicate that AO initially attacks the fluorine portion of the polymers, resulting in a substantial decrease in the near‐surface fluorine concentration. The near‐surface fluorine‐to‐carbon ratios of PVF, PVdF, and PTFE decreased during the 15‐min AO exposure by 68, 39, and 18.5%, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1977–1983, 2004     

X-ray photoelectron spectroscopic study of the ability to monofunctionalize polymer surfaces by low energy atomic bombardment

Low energy atomic bombardment is designed to limit the potentially reactive species to the atoms which are present in a radiofrequency (r.f.) plasma discharge. This might give the ability to monofunctionalize surfaces for specific applications such as biocompatibility. Bombardment of polystyrene and poly(trans)isoprene with nitrogen atoms does not result in the incorporation of any heteroatoms at the polymer surface. Other attempts were made on poly(acrylic acid) and poly(methyl methacrylate) without any results, even though the samples had been activated by argon ion bombardment; the thermalized atoms seem to have insufficient energy to functionalize these polymers. In contrast, ion bombardment performed with low energy nitrogen ions (500–1500eV) is able to incorporate a majority of amine functions. © 1998 Society of Chemical Industry.     

Atomic oxygen erosion resistance of titania–polyimide hybrid films derived from titanium tetrabutoxide and polyamic acid

A series of polyimide/titania (PI/TiO₂) hybrid films have been successfully synthesized based on titanium tetrabutoxide (Ti(OEt)₄), 3,3′,4,4′‐bezonphenone tetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 1,3‐bis(aminopropyl) tetramethyldisiloxane (APrTMOS) by a sol–gel process. The atomic oxygen (AO) exposure tests were carried out using a ground‐based AO effects simulation facility. The chemical structure of PI/TiO₂ films was characterized by Fourier transform‐infrared (FT‐IR) spectroscope before and after AO exposure. The glass transition temperature (T_g) and mechanical properties were examined by dynamic mechanical analysis (DMA) and universal mechanical testing machine, respectively. The tensile strength and elongation of the hybrid film decreased with the increase of TiO₂ content, whereas the T_g increased with the increase of TiO₂ content. The effects of TiO₂ content on the morphology and structure evolvement of PI/TiO₂ hybrid films were also investigated using field emission scanning electron microscopy (FE‐SEM) and X‐ray photoelectron spectroscope (XPS), respectively. The results indicated that a TiO₂‐rich layer resulting from the Ti(OEt)₄ formed on the PI film after AO exposure, which decreased the mass loss rate and obviously improved the AO resistance of PI films. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermodynamics of surface and oxygen vacancy in rare earth stannates by first-principles calculations

The research of nanocrystalline pyrochlores highlights the importance of the surface structure, composition and segregated point defect in their thermal, electrical, optical, magnetic, and catalytic performances. In order to provide a basic view on the surface-related phenomena, thermodynamic stabilities of three low-index (100), (110), and (111) surfaces for A₂Sn₂O₇ (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd), together with their configurations, electronic structures and related oxygen vacancies are investigated using first-principles calculations. The (111) surfaces with A₃SnO₈ and ASn₃O₆ terminations are predicted to be stable due to their low surface energies. Meanwhile, the (110) surfaces with A₂Sn₂O₈ and A₂Sn₂O₆ terminations are found to may also form. For these surface structures, the amount of broken bonds play the main role in their structural stability, and the local coordination environment variation also has minor contribution to it. Moreover, oxygen vacancies are observed to segregate on the surface layer, owing to lower energy of breaking bonds accompanying with oxygen vacancy formation and the larger relaxation space comparing to the counterpart in bulk. These results are expected to provide guidance on optimizing the performances of these compounds through surface engineering.     

Effect of low earth orbit atomic oxygen exposure on epoxy functionalized siloxanes

Epoxy functionalized siloxanes (EFS) are a novel class of UV curable monomers that can be rapidly photopolymerized to give transparent coatings and composites. Thin films of these materials have been subjected to low Earth orbit exposure to atomic oxygen (AO) aboard the space shuttle. It was found that UV cured samples of all four different EFS monomers exhibited excellent AO resistance both to ambient in-flight conditions as well as exposure at 120°C. Based on SEM, STM, XPS, and weight loss data, it was proposed that AO exposure of these materials efficiently produces a thin layer of SiO_x at the surface of the sample. This layer provides a barrier toward further attack by AO. © 1995 John Wiley & Sons, Inc.     

Atomic oxygen resistant coating from poly(tetramethyldisilylene‐co‐styrene)

A polydisilahydrocarbon, namely, poly(tetramethyldisilylene‐co‐styrene), synthesized from dimethyldichlorosilane and styrene in 1 : 0.5 mol ratio under dechlorination conditions was evaluated as an atomic oxygen (AO) resistant coating for polyimide film and C‐polyimide composite. Exposure of the polymer coating on a quartz plate to an AO fluence of 2.1 × 10²¹ atoms/cm² resulted in practically no mass loss, indicating the AO resistance of the polymer. Ten percent solution of the polymer in toluene was applied on aluminized Kapton® polyimide film (125 μm thick) to obtain a coating thickness of ～ 5 μm on the unaluminized surface. In a similar way, the coating was applied on a C‐polyimide composite. The coated and uncoated samples of Kapton® film and C‐polyimide composite were exposed to AO in a plasma barrel system. The uncoated aluminized Kapton® film (125 μm) lost 6.35 mg/cm² when exposed to AO fluence of 1.6 × 10²¹ atoms/cm² whereas the corresponding coated film lost only 0.14 mg/cm² even after exposure to AO fluence of 2.1 × 10²¹ atoms/cm². In the case of the C‐polyimide composite, the uncoated sample lost 63.64 mg/cm² on exposure to AO fluence of 1.8 × 10²¹ atoms/cm² whereas the coated one lost only 0.21 mg/cm² even after exposure to AO fluence of 2.1 × 10²¹ atoms/cm². SEM studies suggest that the coating offers good protection to the substrates. Formation of cracks on some portions of the coating was noticed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2368–2375, 2004     

船舶低表面能防污涂料研究进展

本文论述了低表面能防污涂料的机理和研究进展,展望了仿生技术在低表面能防污涂料研究中的应用前景。     

船舶用低表面能防污涂料的性能研究

以一种有机硅弹性体作基料,制备了低表面能船舶防污涂料,研究了该涂料在不同温度条件下的复涂间隔、与环氧树脂涂料的配套性和防污性能。结果表明,有机硅弹性体漆与环氧防锈漆之间的复涂间隔非常窄,在环氧底漆上喷涂有机硅弹性体时必须严格控制复涂时间;有机硅弹性体漆在高温高湿下,可更好的快速固化;该涂料可以有效防止海洋生物的生长繁殖,且不释放任何重金属有害物质。     

Imidazolium-based ionic thermoplastic polyurethane with low surface energy and antibacterial activities

A series of novel thermoplastic polyurethane elastomers with both low surface energy and antibacterial activity were synthesized in this paper. Firstly, four imidazole salt diols with different alkyl chain lengths at the N-position of imidazolium cation ([CnIm⁺][Cl⁻]) were prepared. Then, imidazolium-based ionic thermoplastic polyurethane elastomers (Si-ITPUs) were formulated by incorporating polydimethylsiloxane and polytetramethylene glycol as a mixed soft segment, 1,4-butanediol and [CnIm⁺][Cl⁻] as a chain extender, and 4,4′-dicyclohexylmethane diisocyanate. The structure, thermal stability, mechanical properties, physical crosslinking density, and the anti-graffiti properties of Si-ITPUs were evaluated. The surface energy and water absorption were evaluated through static contact angle and water resistance tests, respectively. Furthermore, the antibacterial activities against both Staphylococcus.aureus and Escherichia coli were characterized by the plate colony counting method. The results demonstrated that Si-ITPUs possessed surface energy of approximately 23 mN/m, which conferred excellent anti-graffiti and self-cleaning performance. Furthermore, the increase of the alkyl chain length of substitutions resulted in a decrease in the tensile strength but an increase in the elongation at break. Si-ITPU-C₄ exhibited optimized antibacterial activities with an antibacterial rate of more than 99.9% against both S. aureus and E. coli. This novel polyurethane is anticipated to find applications in the medical device industry and food processing sector.     

Damage behavior of atomic oxygen on zirconium carbide coating modified carbon/carbon composite

Zirconium carbide (ZrC) components were induced as coating modification on carbon/carbon (C/C). These ZrC–C/C specimens were investigated after atomic oxygen (AO) exposure for different assessment times, low earth orbit (LEO) ground-based environmental simulator was employed. The results indicate that ZrO₂ is the major production generated by the AO chemical reaction with the ZrC coating. Upon further exposure to AO, the production of ZrO₂ would drop off, then exfoliate easily, due to the mechanical impacting effect. Then the exposed graphite matrix and carbon fiber get corroded. Amorphous diamond-like carbon (DLC) is detected by X-ray photoelectron spectroscopy during AO exposure. Bending strength performance increased by 25% under AO exposure at first 10 h, then dropped by 52.1% from 10 h to 30 h of AO exposure. The AO damage mechanisms of ZrC–C/C composites are revealed.     

粘接低表面能材料的新型胶粘剂研究

详述了用于低表面能材料粘接的新型胶粘剂的制备过程,探讨了低表面能胶粘剂的粘接机理,并讨论了弹性体、三乙基硼烷胺络合物、丙烯酸单体等对低表面能材料胶粘强度的影响.     

低表面能水性聚氨酯的研究

以聚醚210(N210),IPDI(异佛尔酮二异氰酸酯)为基本单体,用硬脂酸单甘油酯封端,合成了一种表面能达33mN/m的低表面能水性聚氨酯树脂,并研究了硬脂酸单甘油酯用量、n(-NCO)/n(-OH)对树脂表面能的影响。     

An atomic force microscopy study of the effect of surface roughness on the fracture energy of adhesively bonded aluminium

The effect of roughening an initially polished aluminium surface using the Forest Products Laboratory chemical etch on the adhesive joint strength has been determined. It was found that while the lap shear strength increased rapidly with etching for short times, the fracture energy did not increase significantly until etching had occurred for at least 15 min. An atomic force microscope (AFM) was used to study the surface/interface morphology and to quantify the surface roughness. The AFM images showed that etching occurs heterogeneously across the aluminium surface and a correlation was found between the fracture energy and the fraction of etched surface. A model based on Griffith's fracture energy approach has been proposed to explain this observation. The lap shear strength was found to be more sensitive to a finer scale roughness which is generated at shorter etching times. Other observations regarding the mode of fracture and the variability in joint strength as a function of the surface roughness are explained on the basis of varying stress concentrations at the crack tip.     

关于低表面能无毒防污涂料的应用研究

本文综述了低表面能无毒防污涂料的国内外研究现状及应用前景，全氟丙烯酸酯低表而能防污涂料由于无毒、环保且性能优越，将成为该类涂料的发展方向。     

纳米氧化物与染土协同抗紫外性能研究

通过研究不同纳米氧化物/染土体系、不同晶型纳米二氧化钛/染土体系以及不同比例的锐钛矿型纳米二氧化钛/染土体系等在紫外-可见光区的透射率,找到具有优异抗紫外性能的纳米氧化物/染土体系,以提高蔺草染土固色质量及保色效果。实验结果表明,添加具有抗紫外性能的纳米氧化物均有利于提高染泥的固色效果;在不同纳米氧化物与染土比例一定情况下,锐钛矿型二氧化钛/染土体系的透过率最低,抗紫外性能最好;无论是对于锐钛矿型纳米二氧化钛/染土体系,还是锐钛矿和金红石型两种晶型的纳米二氧化钛与染土的混合体系,随着体系中纳米二氧化钛含量的减少,体系的抗紫外性能降低;在纳米二氧化钛与染土比例一定情况下,不同晶型的纳米二氧化钛在不同波段的抗紫外性能也有所不同。     

蔺草固色用染土及表面膜层结构分析

对蔺草固色用日本染土进行了成分、粒度及微观结构分析,同时对固色后蔺草表面膜层的微观组织进行了分析研究。结果表明,日本染土成分主要为S iO2、A l2O3占75.6%;染土平均粒度在12.7μm,其中26.92μm以下占90%;SEM分析结果显示,染土为鳞片状结构,未用染土固色的蔺草表面为凹槽结构,固色后染土附着在凹槽内,对草体内的叶绿素起到保护作用,从而达到对蔺草固色的目的。该研究可为新型蔺草染土的设计及开发提供一定的参考。     

分光光度法测定阳离子表面活性剂在砂岩表面的吸附

为测定阳离子表面活性剂十六烷基三甲基氯化铵(1631)在岩石表面的吸附量,利用紫外分光光度法,检测了1631溶液在岩石表面吸附前后的质量浓度,算出1631在岩石表面的吸附量。结果表明,用紫外分光光度法检测阳离子表面活性剂浓度快速准确,确定617nm为测定波长,线性回归方程为y=0 0027x-0 0058,R2=0 9991;不同砂岩表面的吸附平衡时间不同,亲水表面为10h,油表面为16h,砂表面为18h;同砂岩表面的静态饱和吸附量不同,亲水表面是0 7mg·g-1·砂,亲油表面是1 4mg·g-1·砂,油砂表面是6 7mg·g-1·砂;天然岩心动态吸附量为0 8066mg·g-1·砂。     

Effect of sintering on surface chemistry and surface energy of pigmented latex coatings

Drying in the absence of water (sintering) of pigmented coatings made of styrene–butadiene (SB) latex and kaolin clay at different levels of pigmentation was investigated. As found from X-ray photoelectron spectroscopy, sintered coatings showed a higher SB area percent on the surface than did latex with a high glass-transition temperature (T_g) and dried at room temperature. This was a result of latex spreading at the surface. Sintering the high-T_g coatings that were dried at room temperature caused a decrease in the surface energy. Drying in the presence of water (wet coalescing) was compared to drying in the absence of water (sintering). Even though sintered coatings were more porous and had higher gloss, no significant difference was found in the SB/clay ratio at the surface or in the surface energy above the critical pigment volume concentration (CPVC). However, at and below CPVC, the sintering process yielded a higher SB content at the surface and a lower surface energy than the wet-coalescing process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 968–975, 2001