Large-Area High-Contrast Hydrophobic/Hydrophilic Patterned Surface for Robust Electrowetting Devices

Hydrophobic/hydrophilic patterned surfaces (HHPS) are found in nature and are highly desired for practical applications as well. Building hydrophilic patterns firmly on low free energy hydrophobic coatings has been a long-term challenge. The conventional process of reactive ion etching combined with a thermal reflow (RIE-reflow) process results in degradation of both the hydrophobicity and dielectric strength of the hydrophobic coatings. In this work, we propose a reconstructive approach by encapsulating the “damaged” hydrophobic Teflon AF 1600 (AF) surface with a fresh one to keep its hydrophobicity the same as that of a virgin AF surface and, at the same time, enhance the hydrophilicity of patterned microstructures by a local plasma etching method with a self-assembled protection mask. In this way, the extremely high wettability contrast with a large oil/water contact angle difference (Δθo/w) of 175° is reached between the hydrophobic and hydrophilic surfaces. Comparing to the conventional RIE-reflow pr...