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.

Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers

“…During LB transfer, the surface pressure of the DPPC monolayer was rigorously maintained at a constant value using a newly developed droplet manipulation technique based on closed-loop ADSA. 24 Topographical images were obtained using an Innova AFM (Bruker, Santa Barbara, CA). Samples were scanned in air in contact mode with a silicon nitride cantilever with a spring constant of 0.12 N/m and a tip radius of 2 nm.…”

Optical diagnostics of a single evaporating droplet using fast parallel computing on graphics processing units

“…1). It should be noted here that our droplets are very small (i.e., typically smaller than 50 μm in diameter) and hence, as shown in [29,30], they are almost perfectly spheri− cal. Additionally, since the typical droplet charge in our experimental setup is usually below 5·10 5 elementary char− ges [31] we are far from the Rayleigh limit [32], and hence droplet deformation caused by Coulombic forces is not ob− served.…”

Biophysical Assessment of Pulmonary Surfactant Predicts the Lung Toxicity of Nanomaterials

“…The droplet was connected with a motorized syringe that periodically oscillates the adsorbed surfactant film at a physiologically relevant rate and compression ratio by precisely controlling liquid into and out of the droplet. The surface tension and surface area were determined photographically from the shape of the droplet using axisymmetric drop shape analysis (ADSA) …”