Wetting control of simple and complex liquids by application of external electric fields

Wetting is a key phenomenon in interfacial physics that affects the shape and dynamics of droplets on solid surfaces. It can be controlled by employing passive or active methods. The most promising active methods are based on the application of external electric fields, because of their easy implementation and the possibility of manipulating a large variety of liquids. The first part of this Ph.D. thesis deals with different kinds of liquid crystals using methods such as electrowetting on dielectric and dielectrowetting, in particular, focusing on the contact angle variation of liquid crystal sessile droplets to see whether their molecular order somewhat reflects their wetting behaviour. In detail, Chapter 1 introduces the general theory of wetting physics and explains in detail the electrowetting on dielectric and dielectrowetting methods used in the experiments. Chapter 2 gives an overview of liquid crystals, highlighting the physical properties tha characterise the nematic and smectic phases. Chapter 3 reports the measurements and results obtained to study the relationships between the internal molecular order of liquid crystals and their wetting responses using electrowetting on dielectrics and dielectrowetting. The second part of the thesis is, instead, focused on optowetting, an active method based on the electric field induced by illuminating a photovoltaic material, such as lithium niobate. In particular, it deals with the splitting of sessile droplets of water and organic liquids on an engineered z-cut lithium niobate substrate. In detail, the Chapter 4 presents a general overview of fundamental physics of the lithium niobate with special attention on its electrical properties that are involved in the optowetting technique, while the Chapter 5 reports the experiment measurements and main results obtained from the study of droplet splitting of water and organic liquids.