Fiber Raman spectroscopy

Ren B, Li W H, Mao B W, Gao J S and Tian Z Q 1996 Optical fiber Raman spectroscopy combined with scattering tunneling microscopy for simultaneous measurements ICORS 96 XVth Int. Conf on Raman Spectroscopy ed S A Asher and P B Stein (New York Wley) pp 1220-1... 

Bowen, J.M. Sullivan, P.J. Blanche, M.S. Essington, M. Noe, L.J. Optical-Fiber Raman Spectroscopy Used for Remote In-Situ Environmental Analysis US 4,802,761 Assigned to Western Research Institute Filed in 1987. 

Optical Fiber Raman Spectroscopy With the expansion of surface Raman spectroscopy, there is an increasing requirement on the measurement of systems in some very special environments, such as high temperature reactions, explosive, irradiative and combustible systems, or live animals. For the protection of the experimentahst and the instrument, an optical fiber technique is combined with Raman spectroscopy. Optical fibers can be employed to deKver the laser excitation source and collect the Raman signal with greater flexibility. As Raman is intrinsically a weak process, the major consideration of the optical fiber Raman system is to increase the collection efficiency. Typical systems consist of the laser, premonochromator, incident optical fiber, collection optical fiber, and the spectrograph. Additional adaptors are needed to... 

A larger increase of sensitivity in linear Raman spectroscopy of liquids has been achieved with optical-fiber Raman spectroscopy. This technique uses a capillary optical fiber with the refractive index nu filled with a liquid with refractive index He > m. If the incident laser beam is focused into the fiber, the laser light as well as the Raman light is trapped in the core due to internal reflection and therefore travels inside the capillary. With sufficiently long capillaries (1—30 m) and low losses, very high spontaneous Raman intensities can be achieved, which may exceed those of conventional techniques by factors of 10 [8.31]. Figure 8.7 shows schematically the experimental ar-... 

A great increase of sensitivity in linear Raman spectroscopy of liquids has been achieved with the optical fiber Raman spectroscopy. This technique... 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

More recently, Raman spectroscopy has been used to investigate the vibrational spectroscopy of polymer Hquid crystals (46) (see Liquid crystalline materials), the kinetics of polymerization (47) (see Kinetic measurements), synthetic polymers and mbbers (48), and stress and strain in fibers and composites (49) (see Composite materials). The relationship between Raman spectra and the stmcture of conjugated and conducting polymers has been reviewed (50,51). In addition, a general review of ft-Raman studies of polymers has been pubUshed (52). 

Normal transmission IRLD can also be used to characterize polymeric fibers, although scattering can induce sloping baselines. Raman spectroscopy then becomes a convenient alternative. Rutledge et al. have recently probed the orientation in electrospun nanofibers composed of a core of Bombyx mori fibroin and an outer shell of poly (ethylene oxide) [24], The orientation values were low, less than 0.1, as is often the case in electrospun fibers. 

McCreery R.L., Fleischmann M., Hendra P., Fiber Optic Probe for Remote Raman Spectroscopy Anal. Chem., 1983 55 146- 148. 

H.H. Gommans, J.W. Alldredge, H. Tashiro, J. Park, J. Magnuson, and A.G. Rinzler, Fibers of aligned single-walled carbon, nanotubes polarized Raman spectroscopy. J. Appl. Phys. 88, 2509—2514 (2000). 

More examples of forensic applications of Raman spectroscopy have been published recently. It has been used to identify individual crystals of drugs and excipients on paper currency [110], multilayer paint chips, inks, plastics [111], and fibers [112], A study demonstrated the feasibility of quantifying acetaminophen in the presence of many excipient types [113], Other studies seek to identify particulates, such as illicit or abused drugs, in fingerprints lifted at a crime scene [114,115]. 

Raman spectroscopy is a powerful tool for probing orientation, stress, and strain. Galiotis et al. have written a review on the determination of stress and strain in composites and fibers using Raman spectroscopy [179]. Young et al. discuss the complexities of correct interpretation of molecular orientation information encoded in Raman spectra of polymers [180]. Caution and a suitable number of control studies are necessary to prevent faulty conclusions. 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

R.R Paradkar, S.S. Sakhalkar, X. He and M.S. Ellison, On-line estimation of molecular orientation in polypropylene fibers using polarized Raman spectroscopy, Appl. Spectrosc., 55, 534-539 (2001). 

R.M. Patel, A.K. Doufas and R.R Raradkar, Raman spectroscopy for spinline crystallinity measurements. II. Validation of fundamental fiber-spinning models, J. Appl. Polym. Sci., 109, 3398-3412 (2008). 

C. Galiotis and J. Parthenios, Stress/strain measurements in fibers and composites using Raman spectroscopy, in Vibrational Spectroscopy of Biological and Polymeric Materials, V.G. Gregoriou and M.S. Braiman (Eds), CRC Press, Boca Raton, 2006. 

C. Bauer, B. Amram, M. Agnely, D. Charmot, J. Sawatzki, M. Dupuy and J.-P. Huvenne, On-hne monitoring of a latex emulsion polymerization by fiber-optic FT-Raman spectroscopy. Part I Cahbration, Appl. Spectrosc., 54, 528-535 (2000). 

Day, R.J., Robinson, I.M., Zakikhani, M. and Young, R.J. (1987). Raman spectroscopy of stresses high modulus poly(/)-phenylene benzobislhiazole) fibers. Polymer 2S, 1833-1840. 

Galiotis, C. (1993a). A study of mechanisms of stress transfer in continuous and discontinuous fiber model composites by laser Raman spectroscopy. Composites Sci. Technol. 48, 15-28. 

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