Open surface multifunctional droplet manipulation platform fabricated by micromilling

Abstract

Superhydrophobic surfaces patterned with hydrophilic groove structures have promising applications in microfluidics. In this work, hydrophilic groove patterns with stable wettability were created directly on superhydrophobic Al surface by micromilling. Feasibility of applying diverse milled hydrophilic patterns, including dimples, ring grooves and reservoirs connected by winding channels in a variety of droplet manipulations, such as water/oil/air storage, water transport, etc. was tried out. Experimental results showed that the milled dimples and ring grooves on the superhydrophobic background can function as a multifunctional platform for storing micro-liter sized water, oil and gas bubbles; two milled reservoirs connected by a milled channel can serve as a open surface microfluidics to transport liquid using Laplace pressure difference. On the basis of the liquid transport between two reservoirs, more sophisticated liquid handling such as droplet separation and mixing were achieved by transporting liquid among multiple reservoirs. It is thus clear that the micromilling is a quite suitable approach to create complex hydrophilic groove structures on superhydrophobic background for applications to diverse interface-driven microfluidics.