Droplet Isovolumetric Discretization Effect And Its Application On Flow Rate Sensing

Sensors are at the window of any interaction with the physical world,and their success or limitation propels or inhibits the advancement in many fields of science.Recently,owing to the properties of small size,high precision,low power consumption and high throughput,the microfluidics devices have been widely used in the fields of biology,medicine and chemistry.The fluid in the microfluidic microchannel needs to be detected and analyzed in real time and accurately.The flow rate of the fluid in the microfluidic chip is usually nL/min to mL/min,which requires the flow rate device to have a low flow rate detection capability,a high resolution and a large detection range.In this paper,a three-superwettable structure(TSS)with droplet isovolumetric discretization effect is proposed,and a digital droplet micro flow rate sensor is designed based on this effect under variable flow conditions.The digitized microfluidic flow sensor realizes the detection function of the liquid flow by calculating the number of droplets discretized between the two electrodes.Firstly,the structure and the principle of the TSS was introduced:the first layer is a superhydrophobic nozzle surface,the second layer is a superhydrophobic aluminum foil surface and the third layer is a superhydrophilic drainage surface.Secondly,the corresponding theoretical model was established for the discrete process of TSS structure,revealing the mechanism of the isovolumetric discrete effect,which shows the importance of superhydrophobicity and superhydrophilicity of each surface in TSS.The numerical simulation method is also used to simulate the droplet discretization process,which shows the important role of surface wettability in the dispersion in TSS.In addition,through experiments,the effects of liquid flow rate,TSS layer spacing and TSS double-sided film on discrete droplet volume were investigated.The results show that the isovolumetric discretization of the droplets can be maintained when the liquid flow rate is less than 200 ?L/min,and the size of discrete the droplet is only dominated by the gap between the layers in the TSS.As a result,the resolution of the flow sensor can be adjusted by varying the spacing of the layers to accommodate different flow rates detection.Besides,the feasibility of of low flow rate detection of the droplet digital flow sensing was verified by experiments.Finally,the discrete effect of droplets is extended to flexible materials.The integrated flexible TSS chip is preliminarily studied.The detection chip not only has the characteristics of the above flow rate sensor,but also has the advantages of low cost and simple preparation process.In the future,the flow rate sensor can be integrated into a variety of microfluidic chips as a flow detection unit to provide inspirations for the development of multifunctional microfluidic chips.