Formation and Elimination of Satellite Droplets during Monodisperse Droplet Generation by Using Piezoelectric Method

One of the key questions in the generation of monodisperse droplets is how to eliminate satellite droplets. This paper investigates the formation and elimination of satellite droplets during the generation of monodisperse deionized water droplets based on a piezoelectric method. We estimated the effects of two crucial parameters—the pulse frequency for driving the piezoelectric transducer (PZT) tube and the volume flow rate of the pumping liquid—on the generation of monodisperse droplets of the expected size. It was found that by adjusting the pulse frequency to harmonize with the volume flow rate, the satellite droplets can be eliminated through their coalescence with the subsequent mother droplets. An increase in the tuning pulse frequency led to a decrease in the size of the monodisperse droplets generated. Among three optimum conditions (OCs) (OC1: 20 mL/h, 20 kHz; OC2: 30 mL/h, 30 kHz; and OC3: 40 mL/h, 40 kHz), the sizes of the generated monodisperse deionized water droplets followed a bimodal distribution in OC1 and OC2, whereas they followed a Gaussian distribution in OC3. The average diameters were 87.8 μm (OC1), 85.9 μm (OC2), and 84.8 μm (OC3), which were 8.46%, 6.14%, and 4.69% greater than the theoretical one (81.0 μm), respectively. This monodisperse droplet generation technology is a promising step in the production of monodisperse aerosols for engineering applications.

Precise detection of the size of monodisperse droplets considering the fluctuations induced by the droplet generation process

For droplet microfluidics, the electrical-detection method which can precisely detect the size of monodisperse droplets is demonstrated in this paper. In a Flow-focusing microdroplet generator, three pairs of the microelectrodes are allocated along the microchannel, and during the passing-by process of each droplet, both the length, the velocity and the production speed of the droplets can be obtained from the experimental measurements of the time-varying capacitance between each pair of the microelectrodes. Particularly, for different geometries of the Flow-focusing microchannel, the method of the electrical-detection is validated experimentally over a wide range of the typical conditions of monodisperse droplet production. In addition, the droplet size measured by the electrical-detection method is compared with that by the method of image processing, and the detection precision of the electrical-detection method is verified experimentally. Most importantly, by calculating the root-mean-square value of the droplet lengths for three pairs of the microelectrodes, the detection precision of the droplet size can be increased drastically.

OsciDrop: A versatile on-demand droplet generator

Droplet microfluidics has become a powerful tool in many biological and clinical applications to high-throughput encapsulate reactions with single-cell and single-molecular resolutions. Microfluidic chips, such as flow-focusing droplet generators, have become commonplace in microfluidic laboratories. However, the expensive and precision-demanding microfabrication hinders their widespread use in many biomedical laboratories and clinical facilities. Herein, we present a versatile chip-free droplet generator, termed as OsciDrop, for on-demand generating size-tunable droplets with high uniformity. OsciDrop segments the fluid flowing out of the orifice of a micropipette tip into droplets by oscillating the tip under the surface of a continuous oil phase. We investigated the factors influencing droplet generation by examining several control parameters. Results show that flow rate, oscillating amplitude, and frequency are key parameters to on-demand generate monodisperse droplets. Flexible, repeatable droplet generation by OsciDrop was successfully achieved. Importantly, using an optimal asymmetrical oscillation waveform, OsciDrop can controllably generate monodisperse droplets spanning a wide volume range (200 pL - 2 μL). To demonstrate the capability of OsciDrop for chip-free droplet assays, a digital loop-mediated isothermal amplification (dLAMP) was performed to absolutely quantify African swine fever virus (ASFV) DNA templates. The OsciDrop method opens up a feasible and versatile avenue to perform droplet-based assays, exhibiting full accessibility for chip-free droplet microfluidics.

Study on the Technology of Monodisperse Droplets by a High-Throughput and Instant-Mixing Droplet Microfluidic System

In this study, we report a novel high-throughput and instant-mixing droplet microfluidic system that can prepare uniformly mixed monodisperse droplets at a flow rate of mL/min designed for rapid mixing between multiple solutions and the preparation of micro-/nanoparticles. The system is composed of a magneton micromixer and a T-junction microfluidic device. The magneton micromixer rapidly mixes multiple solutions uniformly through the rotation of the magneton, and the mixed solution is sheared into monodisperse droplets by the silicone oil in the T-junction microfluidic device. The optimal conditions of the preparation of monodisperse droplets for the system have been found and factors affecting droplet size are analyzed for correlation; for example, the structure of the T-junction microfluidic device, the rotation speed of the magneton, etc. At the same time, through the uniformity of the color of the mixed solution, the mixing performance of the system is quantitatively evaluated. Compared with mainstream micromixers on the market, the system has the best mixing performance. Finally, we used the system to simulate the internal gelation broth preparation of zirconium broth and uranium broth. The results show that the system is expected to realize the preparation of ceramic microspheres at room temperature without cooling by the internal gelation process.

Mechanical properties of 2D aggregates of oil droplets as model mono-crystals

We investigate the elastic and yielding properties of two dimensional defect-free mono-crystals made of highly monodisperse droplets.

Massive droplets generation for digital PCR via a smart step emulsification chip integrated in a reaction tube

Step emulsification (SE) devices coupled with parallel generation nozzles is widely used in the production of large-scale monodisperse droplets, especially for droplet based digital polymerase chain reaction (ddPCR) analysis. Although...