Chemically Engineered Carbon Nanotube-Polymer Composite Coatings for use as Remote Strain-Sensors
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Chemically Engineered Carbon Nanotube-Polymer Composite Coatings for use as Remote Strain-Sensors Jérôme Halary; John L. Stanford; Peter A. Lovell; Robert J. Young Manchester Materials Science Center, The University of Manchester, Manchester, M1 7HS, United Kingdom. ABSTRACT Carbon nanotubes nanocomposites with unique opto-mechanical properties have been developed as smart coatings. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings and determine local strains on the micron scale directly from stress/strain induced Raman band shifts. Chemically engineered carbon nanotubes and polymer matrices have been developed in order to overcome the limitations highlighted in previous reports. They have proved to be of significance importance in the optimization of the stress transfer between the nanotubes and the polyurethane matrix. INTRODUCTION Since their discovery by Ijima in the early 90s, single-wall carbon nanotubes (SWNTs) [1] have turned into a hot area of research activity due to their exceptional mechanical properties [2-6] and electrical and thermal conductivities [7, 8]. If one of the first areas of interest was in the development of lightweight reinforced materials and/or conducting materials, more recent experimental breakthroughs revealed the great potentiality in developing new generations of sensors: chemical [9] and biological [10] sensors mainly but also strain or pressure sensors [11-14]. Micro-Raman spectroscopy, with its excellent spatial resolution (~1 micron), has been quite extensively used for the measurement of phase stress or strain in crystalline materials [15, 16]. As a material is strained, the interatomic distance changes, giving rise to a change in the interatomic force constant, and therefore a change in the vibrational frequency. The resonant disorder-induced Raman G’ band peak of carbon nanotubes is well known as being dependent upon axial strain [12, 17-21]; the shift with strain being dependent on the optical polarization direction [11, 14]. The aim of this research is to provide a novel high resolution non contact technique for the determination of surface stresses and strains in a wide variety of Raman-inactive engineering components used in both laboratory and in-the-field (external) applications. Filled polyurethanes comprising low volume fraction (0.1 wt. %) of single-wall carbon nanotubes (SWNT-PU) have been developed as strain-sensitive materials. Remote polarised Raman spectroscopy is used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics). If quantitative correlations between Raman band shifts and applied strains have been observed for various substrates, the non linearity of the band shifts at high strains and the scatter of the initial peak position at zero strain induced a loss in sensitivity of the strain mapping technique [14].
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Chemically engineered polyurethane matrices of different hardness have then been developed in order to get a better insight into the infl
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