Micro-winkling can turn a transparent thin-film of zinc oxide (ZnO) to be ‘opaque’ that can be reversed by unfolding to restore back to the clear state. This principle was previously used to make a mechanically tunable window device. However, ZnO thin film cannot make a compliant electrode to enable electrical unfolding due to its insulator nature. This paper reports the use of multilayer thin films of 10nm silver (Ag) and 30nm thick ZnO to form a compliant electrode with electrically tunable transmittance. A dielectric elastomer actuator (DEA) with a pair of such compliant Ag/ZnO thin films on both sides of a polyacrylate elastomeric membrane (3M VHB 4910) makes an electrically tunable window device. The DEA without radial compression of the elastomer has wrinkle-free electrode. Hence, it is clear with a 47% in-line transmittance (for 550nm wavelength light). In the wrinkled form, under 10% radial compression, it becomes opaque (with less than 1% transmittance). A voltage induced areal expansion of 10% radial strain enables the electrical unfolding of the initial wrinkles. In addition, this device continues to work after 4000 cycles of unfolding and microwrinkling of Ag/ZnO. The performance of electrically tunable window device is comparable to the existing smart window technologies.
Milan Shrestha, Anand Asundi, and Gih-Keong Lau, "Electrically tunable window based on microwrinkled ZnO/Ag thin film," Proc. SPIE 10163, Electroactive Polymer Actuators and Devices (EAPAD) 2017, 101631Y (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 29, 2017; Published: 17 April 2017); https://doi.org/10.1117/12.2259918.
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