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Wrinkle meets MEMS: Tunable grating and hydrophobic surface

Multi-layered systems composed of a rigid thin film and an elastomeric base are ubiquitous in nature and in technology [1,2]. When stress is applied to the system, the surface of the system is often deformed in periodical wrinkle patterns due to the mismatch of the stiffness and the length. As reported in [3,4], the periodical patterns result in functional surfaces, such as smart adhesion, hydrophobic surfaces and diffractive gratings. In this paper, we present a tunable grating and a hydrophobic surface using the wrinkle phenomenon. The device is composed of a rigid layer and an elastomeric chamber. The chamber can be inflated pneumatically using oil, and the strain exerted on the device is controllable. By controlling the strain, we achieved a wrinkle pattern with a 10 μm wavelength whose amplitude is tunable from 1.6 μm to 2.8 μm. With this method, a tunable optical grating has been achieved. We have also created a tunable hydrophobic surface by controlling the surface roughness in two dimensions. The contact angle of a water droplet on the device ranged from 110 degrees to 130 degrees. The device can be fabricated with a transparent and flexible material and does not require electrical wires. This paper presents a range of possibilities for a functional wrinkle structure controlled using a MEMS technique.