Develop superhydrophobic surface for droplet manipulation

Abstract

Advances in the field of microfluidics have led to widespread adoption of microfluidic devices used in a wide range of applications, such as clinical diagnosis and biochemical research. One such application is digital microfluidics, which requires manipulation of droplets on a surface that has to be superhydrophobic. This project encompasses 3 parts in making a glass substrate superhydrophobic. First, spray coating a glass substrate using 1% to 3% of Polytetrafluoroethylene (PTFE or Teflon) dissolved in Fluorinert FC-40 solution, a hydrophobic surface with an average contact angle of 121° was obtained, with no change in contact angle at different concentrations. Secondly, spray coating a sandblasted glass substrate with 1% Teflon solution obtained a hydrophobic surface with an average contact angle of 133° in the Wenzel state, which sticks very well to the glass substrate’s surface, as the water droplet does not roll off the surface. Third, by mixing micro/nano size Iron Oxide (FeO) particles at 1% to 10% concentration (with respect to volume of 6 ml) with 1% Teflon solution separately, and spray coating it on a glass substrate, with an average contact angle less than 127°, a hydrophobic surface at low concentration was obtained. Also, with an average contact angle more than 165° with roll-off angle less than 1°, a superhydrophobic surface at high concentration was obtained. Droplets on the surface of the glass substrate coated with micro size FeO particles are in Cassie-Baxter state on the superhydrophobic surface. Droplets on the glass substrate coated with nano size FeO particles are in Wenzel and Cassie-Baxter state on the superhydrophobic surface, as the concentration of the particles increases.