From 'petal effect' to 'lotus effect' on the highly flexible Silastic S elastomer microstructured using a fluorine based reactive ion etching process

A fluorine-based reactive ion etching (RIE) process has been applied on a new family of silicone elastomers named 'Silastic S' for the first time. Excellent mechanical properties are the principal advantage of this elastomer. The main objective of this study was (i) to develop a new process with an electrodeposited thin Nickel (Ni) layer as a mask to obtain a more precise pattern transfer for deep etching (ii) to investigate the etch rates and the etch profiles obtained under various plasma conditions (gas mixture ratios and pressure). The resulting process exhibits etch rates that range from 20 mu m h(-1) to 40 mu m h(-1). The process was optimized to obtain anisotropic profiles of the edges. Finally, it is shown that (iii) the wetting contact angle could be easily modified with this process from 103 degrees to 162 degrees, with a hysteresis that ranges from 2 degrees to 140 degrees. The process is, at present, the only reported solution to reproduce the 'petal effect' (high contact angle hysteresis value) on a highly flexible substrate. A possibility to control the contact angle hysteresis from the 'petal effect' to the 'lotus effect' (low contact angle hysteresis value) has been investigated to allow a precise control on the required energy to pin or unpin the contact line of water droplets. This opens multiple possibilities to exploit this elastomer in many microfluidics applications.