Controlled splitting of liquid droplets is a key function in many microfluidic applications. In recent years, various methodologies have been used to accomplish this task. Here, we present an optofluidic technique based on an engineered surface formed by coating a z-cut iron-doped lithium niobate crystal with a lubricant-infused layer, which provides a very slippery surface. Illuminating the crystal with a light spot induces surface charges of opposite signs on the two crystal faces because of the photovoltaic effect. If the light spot is sufficiently intense, millimetric water droplets placed near the illuminated spot split into two charged fragments, one fragment being trapped by the bright spot and the other moving away from it. The latter fragment does not move randomly but rather follows one of three well-defined trajectories separated by 120°, which reflect the anisotropic crystalline structure of Fe:LiNbO₃. Numerical simulations explain the behavior of water droplets in the framework of the forces induced by the interplay of pyroelectric, piezoelectric, and photovoltaic effects, which originate simultaneously inside the illuminated crystal. Such a synergetic effect can provide a valuable feature in applications that require splitting and coalescence of droplets, such as chemical microreactors and biological encapsulation and screening.

In this work, we report on measurements of the contact angle of sessile droplets of aqueous solutions of a chromonic liquid crystal at different temperatures and concentrations and on different hydrophobic surfaces, and we show that the wettability of this complex fluid can be easily controlled by an external electric field. Specifically, electrically induced variations of the contact angle up to 70° were obtained using external DC voltages. Complementary tensiometric measurements of the aqueous solutions confirmed that the observed variations in the contact angle were mainly related to variations in the surface tension, while they did not show an evident connection with the internal molecular order of the liquid crystal droplets. Our study is relevant in view of the use of chromonic liquid crystals in microfluidic devices, where the control of wettability is an important tool for handling fluid flow.