Study On Precision Liquid Manipulation Of Galinstan-based Microfluidic Inertial Switch

Microfluidic inertial switch uses solid-liquid contact to replace the solid-solid contact of traditional inertial switch,which avoids electrode surface wear and improves stability.It is widely used in automotive safety,weapon control and other fields.Liquid metal with high surface tension,high density and good electrical conductivity,thermal conductivity and fluidity is the best choice of working fluid for inertial switches of linear microchannels.The metal droplets under the action of inertial force/acceleration pass through the valve of the microchannel into the connecting groove and cover the fixed electrodes on both sides,resulting in closing the switch.Compared with the Mercury which is the most commonly used liquid metal,Galinstan has the same excellent performance and is environmentally friendly,non-toxic and not easy to evaporate.Therefore,this thesis takes precision liquid manipulation of Galinstan as the starting point to study the acceleration threshold of Galinstan microfluidic inertial switch,the wettability of wall,the volume control and seal of droplet in the oxygen-free environment.The main research contents of this thesis are as follows:(1)In view of the existing microchannel model,Galinstan is used to replace Mercury as the conductive liquid,and the goal is to achieve the threshold effect similar to the original switch.The wettability of wall,material and volume of conductive liquid all affect the acceleration threshold of switch.Under the same switch model,increasing the volume of fluid or increasing the contact angle of wall can offset the change of threshold caused by the difference of liquid metal properties such as density and surface tension.Hydrophobic treatment on the surface of the microchannel is chosen in this thesis.Through the force analysis of the droplet combined with the structure size of the microchannel,it is calculated that the experimental goal is to increase the contact angle from 135 ° to about 159°.On the other hand,in order to ensure that the influence of droplet volume deviation on the threshold error is less than ±1%,it is necessary to realize the precision control of 0.1μL±3.2% Galinstan.(2)The material of each component of the switch is pretreated,including: 1)The oxide layer on the surface of Galinstan is removed by acid pickling to restore the fluidity and non wettability of the droplets.2)The corrosivity of Galinstan to metal materials is judged to determine the material selection of experimental accessories.3)The substrate and cover plate of PMMA are drophobic treated by nonsolvent induce phase separation combined with low surface energy substances.Hydrophobic nano silica particles are dispersed in the mixture of tetrahydrofuran and absolute ethanol.Under the condition of water bath heating,samples are soaked in the prepared solution and then dried to obtain the superhydrophobic rough surface.The optimal parameter combination is obtained by single factor and orthogonal experiment.The contact angle of Galinstan is increased to 158.8°,the rolling angle and the contact angle hysteresis are both reduced to 2°,which improved the droplet flow performance and the stability of switching threshold.(3)In order to realize the precise and fast packaging of microfluidic inertial switch,the direct ink writing 3D printing process is used to spread the glue.To save the inaccuracy and instability of injecting conductive metal droplet,needle valve system is set up in the glove box.The precision control of the target volume(error range ±3%)is achieved by adjusting the stroke of the needle’s stroke,input pressure and needle’s open time.Then the packaging of the switch is completed by bonding the substrate and the cover plate with UV adhesive,at the same time,the oxidation of Galinstan is inhibited.In order to improve the efficiency of packaging,an integrated dispensing system of gluing and liquid injection is built on the three-dimensional motion platform to provide preliminary exploration for automatic packaging.Finally,the centrifugal acceleration provided by the rotating platform is used to detect the threshold of the switch.Compared with the switch with untreated surface,the threshold of switch with superhydrophobic surface is reduced from 52.54 g to 28.62 g,which is similar to that of the Mercury switch,and both the threshold deviation are less than ±1%.