Electrowetting on dielectrics on lubricating fluid-infused smooth/rough surfaces with negligible hysteresis

Low-voltage electrowetting on dielectrics on substrates with a thin layer of lubricating fluid to reduce contact angle hysteresis is reported here. On smooth and homogeneous solid surfaces, it is extremely difficult to reduce contact angle hysteresis (contact angle difference between advancing and receding drop volume cycle) and the electrowetting hysteresis (contact angle difference between increasing and decreasing voltage cycle) below 10°. On the other hand, electrowetting hysteresis on rough surfaces can be relatively large (~30°); therefore, they are not useful for most of the fluidic devices. In the present report, we demonstrate that using a thin layer of dielectric lubricating fluid on top of the solid dielectric surface reduces the contact angle hysteresis as well as electrowetting hysteresis below 2° on smooth as well as rough surfaces. Electrowetting on lubricating fluid-coated surfaces also show a threshold behavior and the threshold voltage depends on the viscosity of the lubricating fluid. Modified Lippmann equation is used to explain the electrowetting on lubricant-coated surfaces quantitatively. The experimental system can be modeled as two series capacitor, one each for dielectric lubricating fluid and solid dielectric, which jointly govern the electrowetting behavior, whereas the lubricating fluid also minimizes the contact angle hysteresis