Barboza Raouf, Marni Stefano, Ciciulla Fabrizio, Mir Farooq Ali, Nava Giovanni, Caimi Federico, Zaltron Annamaria, Clark Noel A, Bellini Tommaso, Lucchetti Liana
Dipartimento Scienze e Ingegneria dei Materiali e dell'Ambiente e Urbanistica, Università Politecnica delle Marche, 60131 Ancona, Italy.
Medical Biotechnology and Translational Medicine Department, University of Milano, 20054 Segrate, Italy.
Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2207858119. doi: 10.1073/pnas.2207858119. Epub 2022 Aug 1.
We investigated the electrostatic behavior of ferroelectric liquid droplets exposed to the pyroelectric field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase by reducing the temperature from the nematic phase, the liquid crystal droplets become electromechanically unstable and disintegrate by the explosive emission of fluid jets. These jets are mostly interfacial, spreading out on the substrate surface, and exhibit fractal branching out into smaller streams to eventually disrupt, forming secondary droplets. We understand this behavior as a manifestation of the Rayleigh instability of electrically charged fluid droplets, expected when the electrostatic repulsion exceeds the surface tension of the fluid. In this case, the charges are due to the bulk polarization of the ferroelectric fluid, which couples to the pyroelectric polarization of the underlying lithium niobate substrate through its fringing field and solid-fluid interface coupling. Since the ejection of fluid does not neutralize the droplet surfaces, they can undergo multiple explosive events as the temperature decreases.
我们研究了暴露于铌酸锂铁电晶体衬底热释电场中的铁电液滴的静电行为。该铁电液体是一种向列型液晶，其中分子偶极子几乎完全的极性排列产生了一个局部与平均分子长轴共线的内部宏观极化。当通过从向列相降低温度进入铁电相时，液晶液滴变得机电不稳定，并通过流体射流的爆发性发射而解体。这些射流大多位于界面处，在衬底表面展开，并呈现分形分支成更小的流，最终破裂，形成次级液滴。我们将这种行为理解为带电流体液滴瑞利不稳定性的一种表现，当静电排斥力超过流体的表面张力时就会出现这种情况。在这种情况下，电荷是由于铁电流体的体极化产生的，它通过其边缘场和固 - 液界面耦合与下层铌酸锂衬底的热释电极化耦合。由于流体的喷射并没有使液滴表面中和，随着温度降低，它们可以经历多次爆发事件。
