| Droplet control,as a new technology,can accurately control the structure,shape and motion of liquid by using physical,chemical and biological principles,which has the advantages of high accuracy,high time efficiency,good controllability and high flexibility.It is widely used in medical diagnosis,food safety,drug research and development and biological separation.It not only can realize fine control,making the experimental process more accurate and reliable,but also can be used to achieve miniaturization,realizing experiments in a smaller space,thus saving experimental costs.It can also realize automatic operation within a certain range,thus greatly reducing the work of experimental personnel,which has important application value and can provide effective support for experimental accuracy improvement,experimental cost reduction and automatic operation realization.However,in order to further improve the accuracy and transmission efficiency of droplet control,it is necessary to further study the friction and adhesion behavior between droplets and interfaces.In this paper,the friction and adhesion forces of the micro-droplet/injection surface were controlled by adjusting the viscosity of the infused liquid(dimethyl siloxane)and the external voltage,and the mechanism was analyzed in detail in order to obtain better droplet manipulation results.The results showed that when the viscosity of dimethyl siloxane increased from 10 c St to 100 c St,the snap-in force of the micro-droplet/liquid-infused interface decreased from 194 μN to 123 μN,the maximum interaction force decreased from129 μN to 94 μN,and the pull-off force decreased from 101 μN to 82 μN;The interface friction force increased from about 15 μN to 40 μN.In the dielectrowetting experiment on the liquid-infused surface,when the external voltage increased from 0 V to 240 V,the snap-in force increased from 156 μN to about 322 μN,the maximum interaction force increased from120 μN to about 178 μN,and the pull-off force decreased from 85 μN to about 53 μN;The friction force can increase from 15 μN to about 45 μN.The adhesion force/friction of droplets on the liquid-infused surface achieved dynamic adjusting within a 3-fold range.Analysis shows that higher viscosity polydimethylsiloxane has strong shear force internally,and the long chains can enhance hydrogen bonding between micro-droplet/liquid-infused surface.Under the coupling of two kinds of interactions,snap-in force,maximum interaction force and pull-off force decrease with the increase of viscosity,while friction force increases.Under the action of voltage,the micro-droplet produces electrowetting behavior on the liquidinfused surface,and the effective surface energy responds nonlinearly to the voltage,thus realizing the real-time adjustment of solid-liquid interface adhesion force/friction force.Therefore,both the passive way of changing viscosity and the active way of voltage control can effectively adjust the friction and adhesion of the micro-droplet/liquid-infused surface,so that the surface characteristics of the micro-droplet/liquid-infused surface can meet certain requirements.The results of the research can provide technical and theoretical guidance for the optimization design of microfluidic control systems microchannel and the precise delivery of microdroplets. |
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