Polymer films that change color in response to tension

Senior Research Scientist at Japan's National Institute of Advanced Industrial Science and Technology (AIST) has developed polymer films that change color instantaneously and reversibly in response to changes in the tension applied. Kenji Tsuchihara (Senior Research Scientist), the Molecular Smart System Group (Leader: Masaru Yoshida), the Nanotechnology Research Institute (Director: Nobutsugu Minami) of the National Institute of Advanced Industrial Science and Technology (AIST) (President: Hiroyuki Yoshikawa) prepared polymer films on elastic substrates by spin-coating from solutions of substituted polyacetylenes developed. The color of these polymer films changed instantaneously and reversibly when the polymer films were stretched and contracted using a stretching machine. The change in color was repeatable, and it occurred with the application of a small force of manual stretching. This technique is expected to be applied to a tension sensor, which visualizes stress easily and which has been difficult to realize. Unlike polymeric materials that change color in response to heat, light, electric field, and magnetic field; the polymeric materials which change in response to mechanical stimulus, when put to use allow the mechanical stimuli to be visualized easily and inexpensively. Polymerization of acetylene substituted with a substituted phenyl group using [Rh(norbornadiene)Cl]2 as a catalyst produces a polymer in which the main chain is in the cis conformation and has a helical structure. A film of this polymer was prepared by spin-coating from a chloroform solution of this polymer on a colorless elastic sheet. The color of the obtained film of the substituted polyacetylene was yellow at the time of formation. By stretching this film together with the sheet by using a stretching machine, the substituted polyacetylene molecules were oriented along the direction of stretching. Further stretching led to a color change in the film from yellow to red. Measurement of the ultraviolet-visible absorption spectrum indicated an increase in absorption from approximately 500 to 600 nm. Removal of the tension and contracting the film led to the return of the color of the film from red to yellow, and the absorption spectrum agreed with the spectrum before stretching. Thus, the change in color due to stretching and contracting was reversible.
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