1、文章编号:摇 1007鄄8827(2015)05鄄0476鄄05拉曼光谱分析炭纤维表面的微观结构任桂知1,摇 陈淙洁1,摇 邓李慧1,摇 全海宇1,2,摇 吕永根1,3,摇 吴琪琳1,3(1. 纤维材料改性国家重点实验室,上海 201620;2. Texas Tech University, Department of Chemistry and Biochemistry, Lubbock, Texas79409, USA;3. 东华大学 材料学院,上海 201620)摘摇 要:摇 采用拉曼光谱技术研究了 PAN 基炭纤维表面微观结构的异质性。 借助于自制的旋装装置,实现了单根炭纤维纤维的旋转
2、,利用拉曼面扫描技术获得了纤维整个外表面的拉曼光谱。 通过分峰数据处理,得到 II/ IG、IA/ IG、IDi/ IG与 ID/ IG的分布,发现这些结构参数具有较大的波动性,说明炭纤维表面微观结构是不均匀的。 进一步也计算出纤维表面的晶粒尺寸 La在0. 7鄄2. 9 nm 间变化,结构缺陷有沿着纤维轴向取向的趋势。 通过拉曼旋转扫描,揭示出了炭纤维表面的复杂微观结构。关键词:摇 拉曼光谱;炭纤维;表面微观结构中图分类号: 摇 TQ342.+74文献标识码: 摇 A基金项目:国家自然科学基金(60975059);同济大学先进土木工程材料教育部重点实验室(201301);上海市教育委员会科研
3、创新重点项目(14ZZ069).通讯作者: WU Qi鄄lin. E鄄mail: wql dhu. edu. cnMicrostructural heterogeneity on the cylindricalsurface of carbon fibers analyzed by Raman spectroscopyREN Gui鄄zhi1,摇 CHEN Cong鄄jie1,摇 DENG Li鄄hui1,摇 QUAN Hai鄄yu1,2,摇 LU Yong鄄gen1,3,摇 WU Qi鄄lin1,3(1. State Key Laboratory for Modification of Ch
4、emical Fibers and Polymer Materials, Shanghai201620, China;2. Texas Tech University, Department of Chemistry and Biochemistry, Lubbock, Texas79409, USA;3. College of Materials Science and Engineering, Donghua University, Shanghai201620, China)Abstract: 摇 A polyacrylonitrile鄄based carbon fiber monofi
5、lament was characterized by a confocal micro Raman spectrometer withthe aid of a stage that allowed the axial rotation of the fiber so that the whole surface area could be examined. Results indicate thatdisorder is localized and aligned along the axial direction of the fiber. Lavalues in defective r
6、egions are relatively lower than in oth鄄ers. The changes in the amount of amorphous carbon in different regions are significant.Key words:摇 Raman spectroscopy; Carbon fiber; Surface microstructureReceived date: 2015鄄03鄄08摇 Revised date: 2015鄄10鄄08Foundation item : National Natural Science Foundation
7、 of China(60975059); Key Laboratory of Advanced Civil Engineering Mate鄄rials, Tongji University (201301); Research and Innovation Project of Shanghai Municipal Education Commission(14ZZ069).Corresponding author: WU Qi鄄lin. E鄄mail: wql dhu. edu. cnEnglish edition available online ScienceDirect ( http
8、:蛐蛐www. sciencedirect. com蛐science蛐journal蛐18725805 ).DOI: 10. 1016/ S1872鄄5805(15)60202鄄51摇 IntroductionThe properties of polymer fibers are determinedby their structure, especially surface microstructure.For example, the tensile strengths of carbon fibers(CFs) are limited by a spectrum of defects
9、which aredistributed randomly along the fiber axial. The proba鄄bility of encountering a severe flaw becomes greateras the test length of the filament increases1. Defectsand heterogeneity on the surface of fibers are incon鄄trovertible and they are the most important factors af鄄fecting fiber propertie
10、s2鄄4. Slender granule鄄shapeddomain on the longitudinal surface of PAN鄄based CFswas revealed by scanning tunneling microscope, andthe smaller or slender is the domain, the higher tensilestrength is the fibers5. Internal and surface flawshave been identified as source of failure of PAN鄄basedCFs by sca
11、nning electron microscopy of their fracturesurfaces after tension failure1.Besides, surfacecharacteristics of fibers play a key role on fiber鄄matrixinterfacial adhesion and have an important impact onmechanical and ablative properties of fiber鄄reinforced摇第 30 卷摇 第 5 期2015 年 10 月新摇 型摇 炭摇 材摇 料NEW CARB
12、ON MATERIALSVol. 30摇 No. 5Oct. 2015摇composites. Montes鄄Mor佗n et al.6have demonstra鄄ted that there are good correlation between fibre鄄ma鄄trix interfacial shear strength and the degree of surfaceorder. Therefore, it is of great significance to give adeep insight into surface microstructure heterogenei
13、tyof fibers.Raman spectroscopy, sensitive to the sp2and sp3geometries of carbon, has been used to characterizethe microstructure of carbon materials7鄄10. For CFs,ID/ IG, the intensity ratio of two major Raman bands(D and G bands), is proposed as one of the most im鄄portant parameters to evaluate the
14、microstructure het鄄erogeneity11. It has also been demonstrated that theintensity of the D band is lower for the skin than thecore of CFs12. Kobayashi13,14have recently usedsynchrotron micro鄄beam X鄄ray scattering and micro鄄Raman spectral measurements to characterize stressdistribution at the various
15、parts of PAN鄄based CFscaused by structural heterogeneity. Although the Ra鄄man spectroscopy has been employed widely to corre鄄late the microstructure to mechanical properties ofCFs, previous studies mainly focus on the spectralsignals of individual points. To our knowledge, pub鄄lications rarely repor
16、t the microstructure heterogeneityon the whole surface of monofilament. The fact thatthe surfaces of fibers are cylindrical rather than flat,which has hindered a further study.We made a rotating device and used it for char鄄acterization of CF monofilament. Fiber monofilamentscan be rotated for 360毅 w
17、ith the device and thus Ra鄄man spectra can be obtained on the whole cylindricalsurface of a monofilament. This makes characteriza鄄tion of the microstructure heterogeneity of a fibermore representative than focus on individual points.2摇 Experimental2. 1摇 Material and equipmentsAs鄄received PAN鄄based C
18、Fs (7 滋m in diameter,Toray Co. Ltd, Japan) were used in this work.The morphology of the CFs was evaluated usinga scanning electron microscope ( SEM, JSM鄄5600LV, JEOL, Japan).Raman scattering measurements were conductedwith a confocal Raman system (Renishaw InVia Re鄄flex)under ambient condition.The s
19、ystem wasequipped with a Leica microscope, a two鄄dimensionalcharge couple device camera and an automated stagewith a minimum step size of 0. 1 滋m. High鄄resolutiongratings (1 800 lines mm-1) were used with addition鄄al band pass鄄filter optics, and the laser excitationwavelength was 532 nm (argon ion).
20、 All measure鄄ments were made with a backscattering mode using a50伊 microscope objective with a NA value of 0. 75.The illuminated area was less than 1 滋m2. A laserpower of 5% maximum intensity was employed to getthe best signal and to minimize any heating effects.Each point was collected with a step
21、size of 1 滋m, anexposure time of 10 s and a repetition of 10. Thespectrumrangecollectedwasfrom1000to1 900 cm-1, within the first鄄order Raman spectrum ofgraphite鄄based materials15,16.The atomic force microscope (AFM) used is aNanoScope 郁 made in Veeco Company, it workswith an elasticity coefficient a
22、round 48 N/ m and aresonant frequency about 330 kHz.2. 2摇 Rotation methodsA coordinate paper frame (Fig. 1(c) was usedto fix the fiber monofilament straightly by adheringtwo ends of the fiber to the paper cut empty in thecenter, which was then attached to the clapping fix鄄ture of the rotating device
23、 as shown in Fig. 1b. Thedevice rotating is mainly comprised of a crank, adriving gear, a transmission shaft and a driven gear,which was placed under the objective lens for meas鄄urement during rotating (Fig. 1(a).Fig. 1摇 (a) The rotating device under the objective lens;(b) The diagram of the self鄄ma
24、de rotating device;(c) Paper frame used to fix and straighten fiber monofilament.摇摇The detailed testing procedure is described inFig. 2. We chose a line parallel to the fiber axis as thefirst line (denoted as Line1), then 30 points were re鄄corded from P(1,1) to P(1,30) with a step size of774第 5 期REN
25、 Gui鄄zhi et al: Microstructural heterogeneity on the cylindrical surface of carbon fibers . . . . . .摇1 滋m. When the scanning of Line1 was finished, thelaser went back to the beginning position and thecrank was rotated by an angle of about 18毅, followedby the detection of Line 2. The same procedure
26、wasrepeated until the monofilament was rotated for 360毅.Assuming that the cylindrical surface of fiber monofil鄄ament can be unfolded, all the scanned points can bedisplayed in a 30 滋m伊20 滋m microregion as shownin Fig. 3. In this way, whole cylindrical surface of asingle fiber could be determined poi
27、nt by point fromthe Raman spectra.Fig. 2摇 The scanning procedure on the cylindrical surface of a fiber.Fig. 3摇 The scanned points on the unfolded surface of a single fiber.3摇 Results and discussion3. 1摇 The heterogeneity of graphitization degree onwhole surface of a carbon fiberEach Raman spectrum e
28、xhibits a hump鄄like shapewith peaks at 1 360 cm-1and 1 580 cm-1asshown in Fig. 4. The spectrum was deconvoluted withfour peaks located at 1 200 cm-1(D band), 1 360 cm-1(D band), 1 500 cm-1(A band) and1 580 cm-1(G band) to the peak intensities9,17.According to previous researches on carbon鄄based mate
29、rials, D band is usually attributed to an A1gmode and/ or to the breakdown of translational and lo鄄cal lattice symmetries, while G band is widely consid鄄ered as the intrinsic band of graphitic structure18鄄20.“A冶 band is correlated to sp3鄄like structures originatedfrom amorphous carbon or some kind o
30、f organic func鄄tional groups21. D band is tentatively related to bea signature of sp3hybridization formed by carbon at鄄om and a small quantity of heteroatom9.With the help of this self鄄made rotation device,point鄄to鄄point variationsofmicrostructureonthewhole cylindrical surface were derived from thes
31、espectroscopic data for the first time.Fig. 4摇 Raman spectra for point P(1,1) .摇摇 The point鄄to鄄point variations of ID/ IGwere plottedagainst the position of scanned points as shown in Fig.5 (a). One can recognize that ID/ IGdoes not changeobviously in area B, but does significantly in both areaA and
32、 C. This reveals the existence of microstructureheterogeneity on the whole surface of CFs. It is alsoworth noting that disorder structure in area A and Corientates along the axial direction. This can be partlyproved by SEM observation, which demonstrates thatthe defects on surface area A爷 also are a
33、ligned alongfiber length (shown in Fig. 6). Although the scannedareas of SEM and Raman spectroscopy are not exactlythe same, these consistent results reveal somewhat de鄄fect distribution feature. Likewise, ID/ IG, ID/ IG, IA/IG, and IDi/ IGfollow the similar trend as can be dis鄄played in Fig.5. Agai
34、n, it is obvious that the graphiti鄄zation degrees in area A, B and C are quite different,indicating the surface heterogeneity on CFs.3. 2 Crystallite parametersAlong fiber axis, some strips made of graphiteclusters and grains are observed by AFM, as shown inFig. 7. The graphite cluster in鄄plane corr
35、elation lengthcan be calculated from the ID/ IGratio using the rela鄄tionship developed by Tuinstra Keonig15:IDIG=44La(1)Based on the above results, the distribution of Laon the whole cylindrical surface of a CF can be a鄄chieved as shown in Fig. 8. The Lavalues of mostscanned position in area B is ar
36、ound 2.2 nm, which a鄄grees well with the results of Lespade et al.22. How鄄ever, the Lavalues in both area A and C are relativelylower, suggesting that a highly complicated fine struc鄄ture is formed on CFs, which consists of the crystallinezone with various sizes and amorphous region.874摇新摇 型摇 炭摇 材摇
37、料第 30 卷Fig. 5摇 The distributions of (a)ID/ IG, (b)ID/ IG, (c)IA/ IGand (d)IDi/ IGon the whole surface of PAN鄄based CF.Fig. 6摇 SEM image of PAN鄄based CF surface.Fig. 7摇 AFM image of PAN鄄based CF.Fig. 8摇 The distribution of Lavalues on cylindricalsurface of PAN鄄based CF.摇 摇 One possible reason of all
38、these structural hetero鄄geneity is that the main structure of CFs is a turbos鄄tratic graphitic structure rather than a perfect graphitestructure. At the same time, there are inherent flawsin the CF precursor and new defects introduced insubsequent pre鄄oxidation and carbonization11,23.4摇 Conclusions摇
39、摇The microstructure heterogeneity of PAN鄄basedCF monofilament has been characterized by using Ra鄄man spectroscopy with the aid of rotating device to974第 5 期REN Gui鄄zhi et al: Microstructural heterogeneity on the cylindrical surface of carbon fibers . . . . . .摇cover the whole cylindrical surface. Th
40、e Raman in鄄tensity ratios relative to the G band were investigated,showing that the IA/ IGchanges more significantly thanthe other ratios and that the quantity of sp3structurefluctuates significantly along the axial direction of CFmonofilament. Moreover, the heterogeneous micro鄄structure tends to or
41、ient along the fiber axial direc鄄tion. The distribution map of Lasuggests that CFshave a highly complicated fine structure.References1摇 Jones J B, Barr J B, Smith R E. Analysis of flaws in high鄄strengthcarbon fibres from mesophase pitchJ. Journal of Materials Sci鄄ence, 1980, 15(10): 2455鄄2465.2摇 Bur
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