辉光放电中处理聚四氟乙烯表面：Ⅱ,ESR研究PTFE膜自由基

在外部电极电容耦合式反应装置中,对聚四氟乙烯(PTFE)膜进行了辉光放电处理。通过电子自旋共振(ESR)谱研究了PTFE在处理过程中所产生的自由基,着重讨论了温度对ESR谱的影响。最后,以DPPH为内标,测定了处理后PTFE膜的自由基浓度,并考察了自由基在空气中的衰减情况。     

辐射引发和热引发聚丙烯腈纤维的自由基研究

利用电子自旋共振波谱(ESR)研究了聚丙烯腈(PAN)纤维在真空以及空气气氛下经γ射线辐射引发和热引发产生的自由基. 结果显示,室温下辐射诱导产生的自由基为烷基自由基和聚亚胺自由基,辐射产生的自由基随温度升高而衰减,150 ℃时完全消失. 热引发的自由基则依赖于温度和氧气, 当PAN纤维在空气中加热至190 ℃时,开始产生多烯自由基,而且自由基浓度随温度升高而迅速增加;在真空条件下,PAN纤维经加热只产生极少量自由基. 据此推断,热引发自由基是通过热氧化反应产生的,这类自由基位于共轭结构上,其共轭长度也随温度的升高而增加.     

新疆长绒棉辐射效应的谱学研究

用¹³C CP/MAS NMR谱、ESR谱和质子弛豫时间等方法,研究了经γ射线在室温下辐照后新疆长绒棉纤维的辐射效应. 结果表明随着辐照剂量的增加,长绒棉纤维内的自由基浓度明显的增大,并产生了多种自由基的混合物. 由辐照前后的长绒棉纤维的¹³C CP/MAS NMR谱可以得出,随着辐射剂量的增加,C1峰的谱宽趋向增宽,表明了自由基存在的位置. 各类弛豫时间的改变则反映出长绒棉纤维内部聚集态结构和大分子链运动随辐射剂量的变化.     

多自由基体系溶液ESR谱的数据分析

将ER-200D ESR波谱仪ASPECT 3000计算机采集的ESR图谱传输到IBM PC/XT计算机上,通过自行设计的ESR图谱模拟程序ESRSIMU,同屏显示比较,方便、灵活地对多自由基体系溶液ESR一级近似谱进行了模拟,获取了各个自由基的ESR波谱参数和体系中各类自由基的相对浓度等信息.对单个自由基ESR谱的模拟,ESRSIMU的运行速度比BRUKER EPR 3002快近100倍.     

连续波电子自旋共振的二维相关谱

在数学相关分析的基础上,建立了获得连续波电子自旋共振（continuous-wave electronspin resonance, CW-ESR）的二维相关谱的方法. 对光照产生的2-甲基-2-亚硝基-丙烷(2-methyl-2-nitrosopropane, MNP)的自捕捉自由基的一系列CW-ESR谱进行相关分析处理,首次得到了同步和异步的二维电子自旋共振（2D ESR）相关谱. 这种利用数学相关分析方法所得到的2D ESR相关谱将为扩大CW ESR的应用领域及获取更多的有用信息开拓新的途径.     

标准曲线法测定煤中自由基含量

自由基在煤变质过程、煤自燃反应及煤热解和液化中发挥着重要作用,准确测量煤中自由基总量对于研究上述煤的反应机理具有一定的理论意义. 由于单点法测量煤中自由基含量的准确度及精确度不够,该文通过考察ESR测定自由基含量的稳定性和重复性,尝试建立了标准曲线方法测定煤中的自由基含量,得到了满意的结果. 稳定性实验的相对标准偏差（RSD）＜4%,重复性实验的相对准偏差（RSD）＜3%,自由基含量在本实验范围（6.12×10¹⁵~1.47×10¹⁷）内线性关系良好,相关系数＞0.99. 实验结果表明,该方法对煤中自由基含量测定有很好的精密度和准确性.     

γ辐射引发淀粉目由基衰减的动力学研究

用ESR方法研究了红薯淀粉在y射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。     

含萘聚芳醚酮共聚物热处理后产生自由基的ESR谱

萘环摩尔含量20%的聚芳醚酮（PANEK）无规共聚物在340 ℃空气条件下发生交联反应，经过不同时间的热处理后，在室温检测热处理后产生的自由基ESR谱. 它们都有一条较强的单峰，随着热处理时间的增长，自由基ESR谱的幅度增强，将微波功率加大到200 mW, 谱线发生明显的变化，出现两条重叠在一起的谱线，说明含萘环聚芳醚酮在热处理过程中产生了两种不同的自由基. 文中模拟、讨论了热处理过程中产生的两种自由基的归属，一种是RO·自由基，另一种是萘自由基，它们都参与交联反应，RO·自由基起主要作用.     

γ辐射引发淀粉目由基衰减的动力学研究

用ESR方法研究了红薯淀粉在γ射线预辐照下,产生的淀粉自由基特性及其室温下的自由基衰减动力学反应。结果表明在室温条件下,淀粉自由基的相对浓度随辐射剂量的增大而增加。自由基相对浓度的室温衰减用二级反应动力学处理,求得了衰减速率常数和淀粉自由基反应的半衰期。     

ESR自旋捕集技术的发展和在生物医学研究中的应用

ESR是研究自由基最直接和最有效的技术,但是这些自由基必须是相对稳定的,而且要达到一定浓度才能用ESR技术检测和研究. 而生物体系中产生的自由基大部分是不稳定的,这是常规ESR波谱仪无法检测的. 为了克服ESR技术的这一局限性,发展了自旋捕集技术,这是目前研究生物和医学体系中活泼自由基应用最多也是最成功的方法, 每年都有新的自旋捕集剂合成和大量在生物医学应用的报道,为自由基生物医学的研究和发展做出了巨大贡献.  作者建立和发展了捕捉超氧阴离子自由基、羟基自由基、脂质过氧化产生的脂类自由基、一氧化氮自由基和单线态氧及一氧化氮和氧自由基同时检测技术. 利用这些技术开展了细胞、组织产生自由基机理,天然抗氧化剂的筛选及一些重大疾病如炎症、心脏病、老年痴呆症、帕金森综合症,中风,辐射损伤,蛋白质氧化,植物光合系统中产生活性自由基和植物的发病机理研究中的应用,取得了一系列研究结果.     

19F Spin-lattice relaxation and stable radicals in radiation-modified fluoropolymers

Fluorine-19 spin-lattice relaxation of electron-beam-irradiated poly(tetrafluoroethylene) (PTFE) has been investigated in the temperature range from 250 to 315 K. As shown before, in the initial step, radicals are produced by the electron-beam irradiation and chain scission takes place. The concentrations of radicals and chain end groups after irradiation of PTFE strongly depend on the irradiation conditions. Radicals like other paramagnetic species decrease the spin-lattice relaxation times. In addition, decreased polymer chain lengths shift theT ₁ minimum to lower temperatures. Tetrafluorosuccinic acid in solution was used as a model system and paramagnetic copper sulphate CuSO₄ added to quantify the effect on the relaxation times. The shift of the minima inT ₁ versus temperature in PTFE are compared with the chain length determined from high-resolution solid-state nuclear magnetic resonance spectra and with the concentration of paramagnetic species.     

Studies on surface modification of poly(tetrafluoroethylene) film by remote and direct Ar plasma

Poly(tetrafluoroethylene) (PTFE) surfaces are modified with remote and direct Ar plasma, and the effects of the modification on the hydrophilicity of PTFE are investigated. The surface microstructures and compositions of the PTFE film were characterized with the goniometer, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results show that the remote and direct plasma treatments modify the PTFE surface in morphology and composition, and both modifications cause surface oxidation of PTFE films, in the forming of some polar functional groups enhancing polymer wettability. When the remote and direct Ar plasma treats PTFE film, the contact angles decrease from the untreated 108-58° and 65.2°, respectively. The effect of the remote Ar plasma is more noticeable. The role of all kinds of active species, e.g. electrons, ions and free radicals involved in plasma surface modification is further evaluated. This shows that remote Ar plasma can restrain the ion and electron etching reaction and enhance radical reaction.     

Inertial cavitation initiated by polytetrafluoroethylene nanoparticles under pulsed ultrasound stimulation

Nanoscale gas bubbles residing on a macroscale hydrophobic surface have a surprising long lifetime (on the order of days) and can serve as cavitation nuclei for initiating inertial cavitation (IC). Whether interfacial nanobubbles (NBs) reside on the infinite surface of a hydrophobic nanoparticle (NP) and could serve as cavitation nuclei is unknown, but this would be very meaningful for the development of sonosensitive NPs. To address this problem, we investigated the IC activity of polytetrafluoroethylene (PTFE) NPs, which are regarded as benchmark superhydrophobic NPs due to their low surface energy caused by the presence of fluorocarbon. Both a passive cavitation detection system and terephthalic dosimetry was applied to quantify the intensity of IC. The IC intensities of the suspension with PTFE NPs were 10.30 and 48.41 times stronger than those of deionized water for peak negative pressures of 2 and 5 MPa, respectively. However, the IC activities were nearly completely inhibited when the suspension was degassed or ethanol was used to suspend PTFE NPs, and they were recovered when suspended in saturated water, which may indicates the presence of interfacial NBs on PTFE NPs surfaces. Importantly, these PTFE NPs could sustainably initiate IC for excitation by a sequence of at least 6000 pulses, whereas lipid microbubbles were completely depleted after the application of no more than 50 pulses under the same conditions. The terephthalic dosimetry has shown that much higher hydroxyl yields were achieved when PTFE NPs were present as cavitation nuclei when using ultrasound parameters that otherwise did not produce significant amounts of free radicals. These results show that superhydrophobic NPs may be an outstanding candidate for use in IC-related applications.     

Degradation in polytetrafluoro ethylene by 62 mev protons

The aim of our study is to describe the dose dependent proton induced modifications in Polytetrafluoro ethylene (PTFE) by using Fourier Transform Infra-red spectroscopy (FTIR), Thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC) and X-ray diffraction analysis (XRD). The shifting of the main peak along with a decrease in its intensity, the decrease in thermal stability and melting point and the formation of stable free radicals were observed in the polymer by proton irradiation.     

Long-distance oxygen plasma sterilization: Effects and mechanisms

The distribution of electrons, ions and oxygen radicals in long-distance oxygen plasma and the germicidal effect (GE) of Escherichia coli on the surface of medical poly(tetrafluoroethylene) (PTFE) film were studied. The quantity of protein leakage and the production of lipid peroxide in bacterial suspension as well as the state of DNA were measured after sterilization to analyse the inactivation mechanisms. The results showed that the concentration of electrons and ions decreased rapidly with increasing the distance from the center of induction coil, which approximated to 0 at 30 cm, whereas the concentration of oxygen radicals reduced slowly, i.e. decreased 30% within 40 cm. GE value reached 3.42 in the active discharge zone (0 cm) and exceeded 3.32 within 40 cm when plasma treatment parameters were set as follows: plasma rf power at 100 W, treatment time at 60 s and oxygen flux at 40 cm³/min. Fast etching action on cell membrane by electrons, ions and attacking polyunsaturation fatty acid (PUFA) in cell membrane by oxygen radicals are primary reasons of oxygen plasma sterilization in the active discharge and the afterglow zone, respectively. The GE of UV radiation in long-distance oxygen plasma is feebleness.     

Preparing polymer brushes on polytetrafluoroethylene films by free radical polymerization

Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA.     

Comparison of the coating properties and corrosion rates in electroless Ni-P/PTFE composites prepared by different types of surfactants

The effects of the addition of three types of surfactants (cationic, anionic, non-ionic) at different concentrations in the plating bath on the deposition rate, PTFE content and surface morphology of electroless Ni-P/PTFE composite coatings were investigated. It was demonstrated that the cationic and non-ionic surfactants created a uniform distribution of PTFE particles in the coatings. The effects of the surfactant type and concentration on the corrosion properties of Ni-P/PTFE coatings were also studied. The corrosion resistance was increased by the incorporation of PTFE particles into the Ni-P matrix. The level of improvement depended largely on the type and concentration of the applied surfactants.     

Epitaxial crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene

Crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene (PTFE) was studied. Further, cold-drawn polyethylene (PE) was heat treated in contact with drawn PTFE, holding their drawing axes at right angles to each other, and then the morphological change of PE at the interface was studied. Molecular orientation in the surface layer of the PE was examined by observing the molecular orientation of polycaprolactone (PCLn) crystallized on the PE surface.

It was found that PE, PCLn, and nascent nylon 6 crystallize epitaxially on drawn PTFE, which is well known as a polymer having a low energy surface. Intermolecular interaction between PTFE and the overgrown crystalline polymers was explained on the basis of their crystal structures. The molecular orientation of PE in the interfacial region changes from the drawing direction of PE to the drawing direction of PTFE during annealing. It is proposed that PE partially melts during annealing, and nuclei of PE with their c-axis parallel to the molecular axis of PTFE are formed at the interface. Consequently, PE lamellar crystals with their c-axis perpendicular to the original drawing direction grow in the interfacial region between PE and PTFE.     

Effect of Carbon Fiber Surface Oxidation on Tribological Properties of PTFE Composite under Oil-Lubricated Conditions

Air-oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced polytetrafluoroethylene (PTFE) composites under oil-lubricated conditions was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF/PTFE) composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy (XPS) study of the carbon fiber surface showed that, after ozone treatment, oxygen concentration was obviously increased, and the amount of oxygen-containing groups on CF surfaces were increased greatly. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix, and large scale rubbing-off of PTFE was prevented; therefore, the tribological properties of the composite were improved.