Electrowetting on superhydrophobic natural (Colocasia) and synthetic surfaces based upon fluorinated silica nanoparticles

In this study, we look at alternative coatings to be used in DMF EWOD applications, specifically a natural surface, and synthetic fluorinated silica nanoparticle (FSNP) surfaces. Electrowetting on dielectric (EWOD) is a popular digital microfluidic (DMF) actuation approach, where droplets are moved over a series of electrodes. Hydrophobic coating is required to lower surface friction and enhance droplet movement over the surface. FSNPs are synthesized by a modified Stober method, with different sizes of nanoparticles (5 to 150 nm) and various degrees of fluorination (0 to 90%). These FSNP coatings and natural superhydrophobic surface, Colocasia leaf, were characterized with SEM and tested for their EWOD performance, i.e. EWOD voltage and contact angle change. Colocasia leaf required voltages of >300 V for EWOD, whereas the performance of the FSNP coatings with varying nanopartide sizes and degrees of fluorination show EWOD with voltages as low as 20 V. The robustness of the FSNP surfaces was demonstrated by using various organic solvents, and longevity data is also presented. (C) 2015 Elsevier B.V. All rights reserved.