eletrowetting

Electrowetting is the controllable modification of a liquid's wettability on a solid surface by applying an electric field. In the common configuration, a conductive droplet sits on a dielectric layer atop a conductive substrate, with a counter electrode immersed in the liquid. Applying voltage alters the interfacial energies, reducing the contact angle and allowing the droplet to spread. In non-English sources the term is sometimes written eletrowetting.

The phenomenon is often described by the Lippmann–Young equation: cos(theta_V) = cos(theta_0) + (epsilon_0 epsilon_r V^2) / (2 d gamma_lv), where theta_V is the contact angle under voltage and theta_0 is the resting angle. Here, d is the dielectric thickness, epsilon_r its relative permittivity, gamma_lv the liquid–vapor surface tension, and epsilon_0 the vacuum permittivity. The equation applies to ideal, uniform dielectrics with conductive liquids on smooth surfaces.

A widely used variant is electrowetting-on-dielectric (EWOD), enabling digital microfluidics in which individual electrodes are actuated to move, split, or merge droplets. Other approaches explore electrowetting without a dielectric, but require careful control to prevent electrolysis and electrochemical degradation.

Materials commonly employed include fluorinated polymers such as Teflon AF or Parylene as dielectric layers, and conductive substrates such as indium tin oxide (ITO) or metals. Liquids are typically aqueous electrolytes. Actuation voltages are usually tens of volts, chosen to balance speed, energy, and reliability.

Applications span digital microfluidics and lab-on-a-chip systems for chemical and biomedical assays, programmable optical components such as tunable lenses and reflective displays, and thermal management devices. Limitations include dielectric breakdown, contact angle saturation, hysteresis, and unwanted electrochemical reactions; ongoing research aims to improve durability and performance.