Research On Measurement Of Liquid Characteristic Parameters And Control Of Input Power In Acoustic Droplet Ejection

Acoustic Droplet Ejection(ADE)is a non-contact micro liquid transfer technology,which can realize the transfer of nano-liter droplets with high precision and high accuracy.Compared with other micro liquid transfer technologies,ADE technology excites droplets using focused acoustic wave,which is neither limited by nozzles nor polluting droplets,so it has been widely used in the field of life science.Precise control of droplet volume and efficient aggregation of droplets on the collection substrate are very important for ADE systems,both of which depend on ultrasonic power control.However,most of the existing power control methods rely on the tedious power scanning process,which will waste a lot of time in the array transfer of many kinds of reagents.In this paper,the surface tension and viscosity of the reagent are measured using freely decaying oscillations of the acoustically levitated droplets,the input power of the self-focusing ultrasonic transducer is controlled based on the fluid characteristics of the reagent,and the efficient coalescence of droplets is achieved on the collection substrate.The specific research work includes:(1)We set up an ultrasonic liquid transfer system,compiled the calculation program of droplet characteristic parameters,and realized the continuous excitation and dynamic monitoring of nano-liter droplets.The surface tension of ethanol aqueous solutions with different concentrations and the viscosity of glycerol aqueous solutions with different concentrations were measured using freely decaying oscillations of the acoustically levitated droplets.The relative errors of surface tension measurement results were less than 4.1%,and the coefficient of variation was less than 2.1%.The relative errors of viscosity measurement results were less than 4.3%,and the coefficient of variation was less than 3.5%.(2)For the ultrasonic liquid transfer system,a method of power control based on the product of surface tension and viscosity was proposed.According to the range of surface tension and viscosity of reagents commonly used in life science,a power control database model was established by using five different concentrations of dimethyl sulfoxide(DMSO)aqueous solution,which was composed of the product of surface tension and viscosity,the droplet detachment velocity and the ultrasonic input power.The model was verified by a variety of reagents.And finally the excitation of droplets at specific detachment velocities was realized for the reagents with different surface tension and viscosity products.(3)Using distilled water as a reference reagent,droplet coalescence experiments were carried out on glass and polystyrene substrates.Based on the aggregation state of distilled water droplets on these two substrates,the droplet coalescence experiments of several kinds of reagents commonly used in the field of life science were carried out according to the power control method proposed in this paper.The feasibility of measuring the surface tension and viscosity of the reagent using freely decaying oscillations of the acoustically levitated droplets and controlling the ultrasonic input power to realize high efficiency coalescence of the droplets was verified.