Plastics Technology

APR 2017

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The other three devices were inspired mainly by squids' ability to undergo color change, says Zeng. These systems have structures similar to the transparency-change device: two layers composed of a rigid film atop an elastic material. In the lumi- nescent-device system (Fig. 2), UV-shielding materials are used for the rigid film and fluorescent dye was added to the PDMS. When the device is stretched, cracks form in the rigid layer, allowing the fluorescent dyes behind the cracks to be exposed to UV radiation, producing visible fluorescence. When the device is relaxed, the cracks of rigid UV-shielding film close up, and thus the UV-shielding layer can effectively block UV radiation and the system is not luminescent. The color-change device (Fig. 3) has a design similar to the luminescent device. However, in this case, green fluorescent dye is added on the top of the rigid UV-shielding layer and orange fluorescent dye is incorporated in the elastomer layer. Under UV radiation, the device emits green fluorescence in relaxed state and shows orange fluorescence when stretched due to the cracks opening and allowing exposure of the orange dye to UV light. This device is extremely sensitive to mechanical stimuli such as stretching, as it can achieve uniform color change at only 20% strain—a value much lower than in similar devices. The sample's ability to undergo color change is not affected by many cycles of stretching and releasing. Lastly, by adjusting the elastic layer, a pattern was embedded into the elastomer layer (Fig. 4). This pattern was hidden in the relaxed state and revealed when stretched. All the devices have very good reversibility and the mechanical- responsive optical properties are maintained upon numerous stretching/releasing circles. Zeng says these devices could be used in a range of applications. "The transparent-change device can be used in smart windows—a small stretching strain allows the device to turn opaque. For the color-changing devices, they can be used in fields such as encryp- tion, strain sensing, or even toys. We are attempting to scale up the technology in order to commercialize the devices." Check out this article on the Plastics Technology website, PTonline.com, to see video representations of all these devices. ABSOLUTE ROBOT www.absoluterobot.com FULL SERVO ROBOTS PROVEN. AFFORDABLE. EFFICIENT. Max out productivity with the NEW MaxBW10. Check out our entire line of MaxBW full servo robots for machines from 320 to 1,600 tons. • Full servo 3-axis robot • Option for 5-axis full servo A+C • Suitable for IMM's from 500 to 800 tons • Vertical reach of 1500mm • Traverse length of 2500mm • Aggressively competitive price UV-Shielding Layer FIG 4 Embedded-Pattern Device Strong Reflection of Patterned TiO 2 Coating Generated Bright UCONN Logo UV Released Stretched Patterned TiO 2 Coating PDMS Carbon Black PDMS/ Rhodamine EDITOR'S NOTE: All figures in the article were published originally by Nature Communications, Nature Publishing Co., July 8, 2016. 20 APRIL 2017 Plastics Technology PTonline.com M AT E R I A L S Close -Up On Technolog y

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