Meggiolaro Alessio, Cremaschini Sebastian, Ferraro Davide, Zaltron Annamaria, Carneri Mattia, Pierno Matteo, Sada Cinzia, Mistura Giampaolo
Department of Physics and Astronomy, University of Padua, Via Marzolo 8, 35131 Padua, Italy.
Micromachines (Basel). 2022 Feb 18;13(2):316. doi: 10.3390/mi13020316.
The actuation of droplets on a surface is extremely relevant for microfluidic applications. In recent years, various methodologies have been used. A promising solution relies on iron-doped lithium niobate crystals that, when illuminated, generate an evanescent electric field in the surrounding space due to the photovoltaic effect. This field can be successfully exploited to control the motion of water droplets. Here, we present an experimental method to determine the attractive force exerted by the evanescent field. It consists of the analysis of the elongation of a pendant droplet and its detachment from the suspending syringe needle, caused by the illumination of an iron-doped lithium niobate crystal. We show that this interaction resembles that obtained by applying a voltage between the needle and a metallic substrate, and a quantitative investigation of these two types of actuation yields similar results. Pendant droplet tensiometry is then demonstrated to offer a simple solution for quickly mapping out the force at different distances from the crystal, generated by the photovoltaic effect and its temporal evolution, providing important quantitative data for the design and characterization of optofluidic devices based on lithium niobate crystals.
液滴在表面的驱动对于微流体应用极为重要。近年来，人们采用了各种方法。一种有前景的解决方案依赖于铁掺杂铌酸锂晶体，这种晶体在光照时，由于光伏效应会在周围空间产生一个倏逝电场。该电场可成功用于控制水滴的运动。在此，我们提出一种实验方法来确定倏逝场施加的吸引力。它包括分析由铁掺杂铌酸锂晶体光照引起的悬垂液滴的伸长及其从悬挂注射器针头的脱离。我们表明这种相互作用类似于在针头和金属基板之间施加电压所获得的相互作用，并且对这两种驱动类型的定量研究产生了相似的结果。然后证明悬垂液滴张力测量法为快速绘制出由光伏效应及其时间演变在距晶体不同距离处产生的力提供了一种简单的解决方案，为基于铌酸锂晶体的光流体装置的设计和表征提供了重要的定量数据。
