Smart Materials & Structures

We present an electrochromic device (ECD) fabricated using PEDOT:PSS and graphene as active conductive electrode films and a fl exible compliant polyurethane substrate with 1-ethyl-3-methylimidazolium bis(trifl uoromethylsulfonyl) imide (EMI-TSFI) additive, as ionic medium. Th is device with a docile, elastic intermediate substrate along with a transparency controlled PEDOT:PSS fi lm provides a wide color contrast and fast switching rate. We harness wrinkling instability of graphene to achieve a hydrophobic nature without compromising transparency of the ECD. Th is mechanical self-assembly approach helps in controlling the wavelength of wrinkles generated by inducing measured prestrain conditions and regulating the modulus contrast by selection of underlying materials used, hereby controlling the extent of transparency. Th e reduction and oxidation switching times for the device were analyzed to be 5.76 s and 5.34 s for a 90% transmittance change at an operating DC voltage of 15 ± 0.1 V. Strain dependent studies show that the performance was robust with the device retaining switching contrasts even at 15% uniaxial strain conditions. Our device also exhibits superior antiwetting properties with an average water contact angle of 110° ± 2° at an induced radial prestrain of 30% in the graphene fi lm. A wide range color contrast, flexibility, and antiwetting nature of the device envision its uses in smart windows, visors, and other wearable equipment where these functionalities are of outmost importance for developing new generation of smart interactive devices.