Raman-Active Nanostructured Materials for Use as Novel Stress-Sensitive Polymeric Coatings
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Q10.11.1
Raman-Active Nanostructured Materials for Use as Novel Stress-Sensitive Polymeric Coatings Jérôme Halary; John L. Stanford; Peter A. Lovell; Robert J. Young Manchester Materials Science Center, UMIST, Manchester, M1 7HS, United Kingdom. ABSTRACT Nanocomposites and nanostructured polymers with unique opto-mechanical properties have been developed as smart coatings for use in a novel, high resolution, and non-contact strainmeasuring application. Remote polarized Raman spectroscopy has been used to monitor optical strain sensitivity of deformed coatings (deformation micromechanics), and determine local strains on the micron scale directly from stress/strain induced Raman band shifts. The research is aimed at providing a novel high-resolution non-contact technique for the determination of surface stresses and strains in a wide variety of engineering components used in both laboratory and in-the-field (external) applications. INTRODUCTION Smart materials can be defined as materials that incorporate the functions of sensing, actuation and control. In this study, we aimed to develop a novel high-resolution, non-contact Raman technique to measure surface stresses and strains of a wide range of Raman-inactive engineering components. It is widely recognised that some crystalline materials are capable of undergoing stress/strain induced Raman band shifts [1, 2]. 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. Following the peak position enables the stress or strain applied to that material to be measured. A recent study in Japan [3], has reported the development of PbO coatings for strain measurement applications. Such coatings, however, are brittle (breaking strain ~ 0.5 %) and have relatively small strain-induced Raman band shifts (~ -2 cm-1 / % strain) with substantial errors arising from the weak Raman scattering. The present study is concerned with the development of stress-sensitive coatings by combining materials that undergo resonant Raman scattering within high performance polymer matrices. Polyurethanes were therefore used because of their excellent and wide-ranging physical properties and ease of processing. Two types of coatings were developed: (i) microphaseseparated copolyurethanes (DA-coPU) where the Raman active species are nanoscale-dispersed diacetylene-containing hard segments (DA) that are produced in situ [4] and (ii) polyurethane nanocomposites (SWNT-PU) filled with dispersed HiPco single-wall carbon nanotubes. Polydiacetylenes [5, 6] and DA-coPU systems have been extensively studied in the past fifteen years [7-10], whereas most research based on embedded nanotubes is usually centred on epoxy resins or PMMA as matrices [11-16]. We will report our work on SWNT-PU nanocomposites, only referring to work on DA-coPU when necessary. Details of the research upon DA-coPU can be found in [4].
Q10.11.2
PRINCIPLES In the case of a perfectly bonded coating of negligible thickness,
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