Study of repeated damage-recovery of hydrophobic coatings for EWOD devices

The degradation of the hydrophobic coatings used in electrowetting-on-dielectric (EWOD) device is inevitable due to the external environmental factors. The single damage-recovery cycle of the hydrophobic coating has been studied by other research groups. However, there is a lack of research demonstrating the possibility of multiple damage-recovery cycles. Hence, this paper investigates the changes in the driving performance of an electrowetting device due to repeated damage-recovery cycles of CYTOP (CTX-809SP2) coatings. Samples were damaged by water droplet impacts one drop per second at a fixed height for 10 days. Contact angle(CA) and contact angle hysteresis(CAH) of samples were measured on a daily basis. The damaged samples were then heat-treated at 200 degrees celcius in an oven for 24 hours for recovery. CA and CAH of heat-treated samples were measured to demonstrate the recovery of the CYTOP coatings. After two times of damage-recovery cycles, it found that EWOD actuation performance has been significantly degraded. To analyze the reasons, the surface morphology of the CYTOP coatings was observed using atomic force microscopy (AFM). This study is expected to be useful for future applications of hydrophobic coatings in EWOD devices.