Electrowetting on Dielectric: A Low Voltage Study on Self-Assembled Monolayers and Its Wetting Kinetics

A systematic study of electrowetting using alkanethiolate self-assembled monolayers (SAMs) as a dielectric layer is presented. SAMs surfaces are characterized by means of ellipsometry, and contact angle measurement. It is demonstrated that droplet spreading can be induced by a much lower voltage (4 volts), although SAMs appear to be irreversible at this operating potential. Experimental results show that the kinetics of contact angle of a NaCl solution droplet significantly depend on SAMs functional group, but not the hydrocarbon chain length. The modified molecular kinetic model employed to produce the fitted curves is in good agreement with the experimental results. A linear relation between the viscous parameter of the model and the number of hydrocarbon chain length of the thiol layer can be found. It appears that the friction force is also significantly influenced by the functionality of SAMs.