The Research Of The Droplets’ Generation And Manipulation Technologies In The Microfluidics

Microfluidics has been widely used in precision manufacturing,material synthesis,life science,bio-medicine and etc.Based on the technologies of droplets generation and manipulation,these applications can be realized.However,there were still many problems in these technologies,such as the volume deviation among the generated droplets and the difficulty to re-programming the positions of the droplets without special physical characteristics by non-contact manipulation.These problems hindered the improvement of the microfluidics technologies severely.By studying the fluid characteristics acted by multiphysical fields,novel methods of precise adjusting the micro-droplets’ volume and reprogramming the micro-droplets’ position by non-contact manipulation were proposed.The main contents of this dissertation were arranged as follows:(1)On the basis of the theory of interfacial tension,a novel method of micro-droplet generation by liquid bridge broken up was proposed.The method was suitable for generating both Newtonian and non-Newtonian fluids.Firstly,the relationship among the parameters in droplet formation process was theoretically analyzed and the mechanical mechanism of liquid bridge fracture was built.By numerical calculation and experimental study,the effectiveness of this method was verified.By experimental study,the relationship between the minimum size of the generated droplet and the tube’s diameter,the surface tension of the fluid,the external force acted on the liquid bridge was measured,respectively.Then,by experiment the method was also suitable for generating the non-Newtonian fluid droplets.Finally,by this method,the magnetic actuator was fabricated.(2)In order to solve the problem of large coefficient of variation among the generated droplets’ volume,on the basis of electrolysis,a novel method to accurate adjustment the droplets’ volume and p H volume simultaneously was proposed.Firstly,the mechanical model of droplet automatic detachment from electrode and the minimum energy model of bubble bursting droplet were established.Through numerical fitting and theoretical calculation,the relationships: the volume of the droplets on the substrate vs diameters,the distance between two electrodes vs the generated droplets’ diameters by electrolysis,the volume consumption of the droplets vs the p H value of the droplet were established.Finally,the effectiveness of the proposed method is verified by experimental research.(3)In order to solve the problems existing in the traditional non-contact manipulation method of re-programming the microdroplets positions,based on the acoustics streaming,a kind of ultrasonic cantilever structure was proposed.Firstly,the relationship between the noncontact manipulation force and the velocity of the fluid in the acoustic streaming fields was theoretically analyzed.And the mechanical model of the droplets’ non-contact manipulation was established.The validity of the proposed method was proved by the finite element analysis and experimental study.In addition,by experiments,the performance of the ultrasonic cantilever structure(driving voltage range,non-contact control ability and the maximum influencing distance to the droplet)were studied.Finally,based on the experimental results,the targeted merging of micro-droplets was realized.In the experiments,the droplets were made by DI water,which did not have special physical properties.Thus,this method was suitable to noncontact manipulate all kinds of droplets.(4)In order to solve the problem that the non-contact manipulation force of the ultrasonic cantilever structure was small,based on the acoustic streaming,an ultrasonic cantilever structure with T-shaped end was proposed.Firstly,based on the theory of mechanical vibration and acoustic flow field,the relationship between the shape of the end of the ultrasonic cantilever structure and the control force was theoretically deduced.The deduced relationship and the effectiveness of the proposed method were verified by the FEM calculation and experimental study.In addition,by experiments,the performance of ultrasonic cantilever structure with Tshaped end(control ability and the maximum influence range on the droplet)were explored.Finally,on the basis of the experimental results,droplet merging,droplet patterned arrangement and droplet array fabrication were realized successively.Finally,the contents of this dessertation were summarized and the future research works were look forward.