AC Electrowetting of NaCl Droplet on Parylene Surface: A Theoretical and Experimental Study

The AC electrowetting of NaCl droplet on surfaces of parylene coatings was mathematically modeled, theoretically analyzed in energy minimization principle, experimentally evaluated via orthogonal experimental design and with the lab-built platform.The influence of AC voltage/frequency and praline thickness on the electro-wetting properties was investigated.The results show that AC voltage/frequency and parylene thickness all had a major impact.For instance, as AC voltage increased, the contact-angle, on surface of parylene with fixed thickness, decreased to saturation in parabolic way;as the thickness increased from 0.5 to 5 μm, the AC saturation voltage increased from 25 to 65 V;as AC frequency increased from 50 to 500 Hz, the saturation voltage decreased in an inverse-proportion;however, high frequencies, close to droplet's natural-frequency, induced a dynamic instability, because of resonant oscillation of NaCl droplet.Optimal contact-angle of 75.8° occurred on 0.5 μm thick parylene coating at 25 V/250 Hz.