Study of cyanoethyl pullulan as insulator for electrowetting

In this paper, the dielectric and electrowetting properties of cyanoethyl pullulan (CEP) are studied as the insulator in electrowetting on dielectric (EWOD) device. The CEP film is formed by spin-coating and low-temperature annealing in atmosphere. The characterization results show that CEP can serve as the dielectric of EWOD with a high dielectric constant of 18 and a great electrowetting performance when annealed at 100 °C in atmosphere. The reversibility, stability, polarity-dependence, and frequency-dependence of electrowetting on CEP are fully investigated. The spin-coated CEP exhibits little polarity-related electrowetting while having better driving performance under negative-potential. Frequency-related electrowetting is more sensitive at low-frequency alternating current (AC) potentials than at high-frequency ones. It also shows reversible and stable electrowetting with a small irreversibility of 2° after a 700-cycle test. Based on the above results, an EWOD device with 1 μm thick CEP dielectric layer is fabricated. The EWOD device successfully manipulates water droplet at a low driving voltage of 20 V and a large velocity under low voltage of DC or AC signals with different frequencies. The easy fabrication and excellent performance of CEP qualifies it as a superior dielectric material in the future EWOD devices and lab-on-a-chip system.