Oxygen plasma treatment time induced hydrophilicity of polydimethylsiloxane (PDMS) thin films for liquid lenses application

Abstract

Poly (dimethylsiloxane) (PDMS) has excellent physical and chemical properties, which are widely used for hydraulic fluids, lithography, and many applications. However, the hydrophobic property of PDMS limits some applications such as the insulating protective layer of electrodes for adaptive liquid lens devices. The oxygen plasma treatment can improve the hydrophilic of the PDMS surface, which is the appropriate surface for liquid lens application. In this paper, we present the oxygen plasma treatment time dependence of the hydrophilicity on the surface of PDMS thin films. The different thicknesses of PDMS thin films were treated by oxygen plasma at different treatment times. The contact angle of glycerol on the PDMS thin films with a thickness of 15 ± 1.17 µm and 43 ± 1.44 µm was initially 104 and 76.7°, respectively. As the treatment time increased, the contact angles of both PDMS thicknesses were gradually decreased. The results show that at an oxygen plasma power of 200 W, an extended treatment time would allow the PDMS surface to be hydrophilic. Moreover, the hydrophilic transformation rate of PDMS thin film is rather more rapid than that of PDMS thick film. The oxygen plasma treatment time and thickness of PDMS film are the key conditions for the adaptive liquid lens application.