Development of New Coating Material for Measuring Local Strain by Micro-Raman Spectroscopy
Michinari FUTAMURA, Hideki HAYASHI, Koji HIRANO and Takushi MIYAKE
Abstract:Although micro-Raman spectroscopy is a useful method as a strain probe with high spatial resolution, this method can not be applied to certain isotropic materials, such as less oriented polymers. To overcome the limitation diacetylene-containing copolymers, which were shown to have Raman band shift with tensile strain, were coated on substrates as an optical strain gage. In this study, diacetylene-containing copolyurethanes were prepared from new compositions by employing polycaprolactone instead of poly(propylene glycol). A solution of the copolymer was coated onto a single filament of an aramid fiber and cross-polymerized by heat treatment. And then, Raman spectra from the coating and the fiber substrate at the same point were measured simultaneously during a tensile test. The Raman frequency of the carbon triple bond (C≡C) in the cross-polymerized polymer coated on the fiber was found to follow closely the local strain of the fiber substrate. The Raman frequency of the coated polymer shifted with strain at a rate of -6.6cm-1/% and held an approximate linear relationship up to 2% strain. Both of the shifting rate and the linear range were improved by replacing ether bonds with ester bonds in the copolyurethans used as matrices. Key Words:Diacetylene-containing copolymer, Strain-sensitive coating, Microscopic strain measurement, Optical strain gage, Micro-Raman spectroscopy