Electrowetting Technique for Measuring the Thickness of Spin-Coated Hydrophobic Fluoropolymer Films

For use as an analysis tool, the electrowetting technique was explored for measuring the thickness of thin hydrophobic dielectric films that were prepared by spin-coating a fluoropolymer resin in various weight percents on glass substrates coated with conductive tin-doped indium oxide (ITO-glass). We found that the film thickness was well fitted to a power law, yielding an exponent of 1.5, and that the results were in good agreement with those from the empirical deposit equation for the spin-coating technique. The X-ray reflectivity measurement also supported this method being very precise with a relative uncertainty of 9.2%, because this uncertainty is on the order of the roughness. These results indicate that this method can be used to find the thickness of thin hydrophobic and dielectric films on various conducting substrates. Conversely, the results of this report support the fact that the classical Young-Lippmann equation well describes the electrowetting on thin hydrophobic films well.