title: Automated Droplet Manipulation Using Closed-Loop Axisymmetric Drop Shape Analysis.
abstract: Droplet manipulation plays an important role in a wide range of scientific and industrial applications, such as synthesis of thin-film materials, control of interfacial reactions, and operation of digital microfluidics. Compared to micron-sized droplets, which are commonly considered as spherical beads, millimeter-sized droplets are generally deformable by gravity, thus introducing nonlinearity into control of droplet properties. Such a nonlinear drop shape effect is especially crucial for droplet manipulation, even for small droplets, at the presence of surfactants. In this paper, we have developed a novel closed-loop axisymmetric drop shape analysis (ADSA), integrated into a constrained drop surfactometer (CDS), for manipulating millimeter-sized droplets. The closed-loop ADSA generalizes applications of the traditional drop shape analysis from a surface tension measurement methodology to a sophisticated tool for manipulating droplets in real time. We have demonstrated the feasibility and advantages of the closed-loop ADSA in three applications, including control of drop volume by automatically compensating natural evaporation, precise control of surface area variations for high-fidelity biophysical simulations of natural pulmonary surfactant, and steady control of surface pressure for in situ Langmuir-Blodgett transfer from droplets. All these applications have demonstrated the accuracy, versatility, applicability, and automation of this new ADSA-based droplet manipulation technique. Combining with CDS, the closed-loop ADSA holds great promise for advancing droplet manipulation in a variety of material and surface science applications, such as thin-film fabrication, self-assembly, and biophysical study of pulmonary surfactant.
authors.affiliation: Department of Mechanical Engineering, University of Hawaii at Manoa , Honolulu, Hawaii 96822, United States.
authors.forename: Kyle
authors.initials: K
authors.lastname: Yu
authors.affiliation: Department of Mechanical Engineering, University of Hawaii at Manoa , Honolulu, Hawaii 96822, United States.
authors.forename: Jinlong
authors.initials: J
authors.lastname: Yang
authors.affiliation: Department of Mechanical Engineering, University of Hawaii at Manoa , Honolulu, Hawaii 96822, United States.
authors.forename: Yi Y
authors.initials: YY
authors.lastname: Zuo
mesh_terms: D001331:Automation; D057446:Hydrodynamics; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D013501:Surface-Active Agents