Characterization of the recently observed polarization-induced Rayleigh Instability of ferroelectric droplets

Liquid crystals (LC) refer to an intermediate state of matter between the liquid and crystalline states. Due to their peculiar properties, these materials have gained wide applicability in the fields of optics, display technology, and biophotonics. For years, we have only known about the nematic, smectic, and cholesteric mesophases of liquid crystals (especially the thermotropic liquid crystals). However, Born et al., in their first theory of liquid crystals published more than a century ago, envisioned the existence of polar ferroelectric fluid in which the identity between the positive and the negative director axes (n and -n) is lost. Amazingly, Chen et al. in 2020 unexpectedly discovered the predicted polar nematic phase and termed it “ferroelectric nematic phase” of LCs. This is a groundbreaking discovery since the combination of fluidity in ferroelectric fluid and its polar coupling to electric fields is opening the gate to a whole new world of phenomena, which are rapidly becoming the focus of the liquid crystals and soft material scientific communities, as demonstrated by the large number of scholarly articles already published on the subject. In this scenario, recent experiments devoted to characterize the behavior of sessile ferroelectric nematic droplets on ferroelectric solid substrates, showed that the combination of fluidity and polarity gives rise to a droplet electromechanical instability induced by the coupling of the LC polarization with that of the solid substrate. With the aim of characterizing this phenomenon, in my thesis I investigated the behavior of ferroelectric nematic liquid droplets deposited on lithium niobate ferroelectric crystals, in different configurations. The configurations have been chosen so to generate potentially different coupling between the polarizations of the liquid and solid materials. Results show that the electromechanical instability of ferroelectric nematic droplets is indeed deeply affected by the way in which the LC polarization interacts with the lithium niobate polarization. This is a novel research and its results could be significant to the scientific communities in the fields of biophotonics, optics, and display technology and due to the unique polarization and fluidity properties of the ferroelectric nematic fluid, it might also provide basis for novel electrohydromechanical applications.