Photovoltaic charge lithography for droplet transport and electrowetting on passive dielectric substrates

Photovoltaic charge lithography is an innovative method for printing surface charges from an illuminated iron-doped lithium niobate crystal stamp onto passive dielectric substrates. We hypothesize that this approach can be effectively utilized for droplet manipulation, including electrowetting and droplet transport, offering high reconfigurability similar to optical techniques and avoiding the need for the presence of photosensitive materials in the main platform, simplifying the design of the system and expanding its practical applicability.

We tested photovoltaic charge lithography on a variety of dielectric substrates with different wetting properties. Using incoherent illumination in an air atmosphere, we examined the method's versatility by exploring the effects of varying light exposure on electrowetting and dielectrophoretic droplet attraction. Numerical simulations were also conducted to investigate the interactions between the printed surface charges and the droplets, providing a deeper understanding of the underlying mechanisms.

Our results confirmed the effectiveness of photovoltaic charge lithography for manipulating droplets on diverse dielectric substrates. The method enabled complex functionalities, including light-exposure-tailored electrowetting, droplet transport of single and multiple consecutive droplets (even uphill), and controlled coalescence. Furthermore, the technique proved to be capable of printing surface charges on flexible polymeric substrates, demonstrating its broad applicability. Numerical simulations supported the experimental observations by offering valuable insights into the interactions between the printed charges and the droplets.