Application Cases

Experiment Name: Fusion Experiment of Bichemical Droplets

Research Direction:Microfluidics is an emerging technology that has developed in recent years. It integrates micro- and nanochannels onto a chip of just a few square centimeters and controls and manipulates the fluids and dispersed micro- and nanoparticles within the channels by applying external physical fields. Due to the rapid development in the field of microelectromechanical systems (MEMS), people now can fabricate highly integrated, cross-scale, and highly controllable microfluidic chips using MEMS processing technologies. As a result, it has been widely used in multiple fields such as biomedical, new materials, and cutting-edge engineering. Droplet microfluidics, as an important branch of microfluidics, controls immiscible two-phase or multiphase fluids in microfluidic chips to prepare and manipulate independent, monodisperse droplet units. It is mainly used in cutting-edge fields such as biochemical analysis, micro- and nanoparticle synthesis, and precision microreactors, for example, in single-cell detection, biomacromolecule analysis, and nanoparticle preparation.

Experiment Purpose:To investigate the voltage required for droplet fusion as the frequency of the electrical signal increases under a fixed electrical conductivity. To determine the fusion region of droplets under different parameters and the voltage and frequency fusion regions of droplets under different electrical conductivities, providing a reliable reference for parameter selection in practical applications.

Testing Equipment:Fluorescence microscope, signal generator, micro-injection pump, ATA-2021 high-voltage amplifier, digital camera, microfluidic chip.

Experimental Process:After the signal generator applies sinusoidal signals of different frequencies, the signals are amplified to 10-60 V by the power amplifier. Randomly arranged droplets first undergo rotation, with the line connecting the centers of the two inner nuclei of the droplets becoming nearly parallel to the direction of the electric field. Subsequently, the inner nuclei of the droplets fuse, but the outer shell remains intact under an appropriate voltage. If the voltage is too high, the outer shell of the droplet will also rupture, leading to a failure in controllable droplet fusion. However, the rupture of the droplet's outer shell provides a method for the controllable release of the inner nuclei. After fusion, the external electrical signal is removed. Due to the higher viscosity of the intermediate phase compared to the inner phase, the inner nuclei appear elliptical immediately after fusion and then return to a spherical shape under the action of surface tension. In this experiment, the electrical conductivity of both the inner and outer phases is 8 mS/m, the electric field frequency ranges from 10 kHz to 500 kHz, and the amplitude is 40 V.

Experimental Results:The experiment found that droplets can fuse within the frequency range of 10 kHz to 400 kHz of the electrical signal, and the trends of the low-voltage threshold and high-voltage threshold are similar. When the frequency is less than 140 kHz, both the low-voltage and high-voltage thresholds increase with increasing frequency, with the slope of the curve gradually increasing. When the frequency exceeds 140 kHz, the high-voltage threshold reaches a plateau and no longer increases with increasing frequency, while the low-voltage threshold continues to increase with frequency until the low-voltage and high-voltage thresholds intersect at around 400 kHz. For a specific electric field frequency, there is a specific voltage range for the fusion of the droplet's inner nuclei. The experimental results show that the voltage range for droplet fusion,, first increases and then decreases, reaching a maximum value of 22.5 V at a frequency of 100 kHz. A frequency of 100 kHz is the optimal frequency for droplet fusion under the experimental conditions.

This phenomenon of voltage increasing with frequency can be explained by two effects. First, the flow on the surface of the droplet's inner nuclei moves from the poles of the intermediate phase towards the two nuclei, thereby hindering the fusion between droplets. This flow increases with the increasing frequency of the electrical signal, thus having an inhibitory effect on fusion. Second, the deformation of the droplet's inner nuclei decreases with increasing frequency at the same voltage. Therefore, to achieve the same degree of deformation, the voltage needs to be correspondingly increased with increasing frequency to further drive the thinning of the film between the inner nuclei to a certain extent, enabling droplet fusion.

Voltage Amplifier Recommendation: ATA-2021B High-Voltage Amplifier

Figure: Performance Parameters of the ATA-2021B High-Voltage Amplifier

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