液体弹珠碰撞固着液滴的影响因素及动力学分析

Influence factors and kinetic analysis of liquid marbles colliding with sessile droplets

液体弹珠具有不润湿/不黏附,以及与外界进行选择性物质交换等特性,可以作为微量液滴承载体,广泛运用于微流控、化学/生物微反应器等新兴领域.碰撞可作为弹珠进行物质传递的一种操控方法,区别于液滴-液滴或弹珠-弹珠的碰撞,弹珠与液滴的碰撞行为更为丰富与复杂,对其的研究可为以弹珠为媒介的物质的有效传递奠定理论基础.本文利用高速摄像机拍摄技术,捕捉了液体弹珠与固着液滴碰撞过程,探究了不同奥内佐格数(Oh)以及壁面亲/疏水性(接触角:q为35.4°-124.5°)下弹珠与液滴之间的碰撞过程.结果表明:在亲水壁面时,以翻越的形式与液滴结束碰撞;当改用疏水壁面后,以回弹行为取代翻越;当壁面疏水性提高接触角达到q=124.5°时,有效碰撞面积增大,碰撞后在界面产生的波动使弹珠表面的颗粒迁移,出现裸露区域,形成液桥后快速完成聚结-合并(聚并).弹珠与固着液滴碰撞后,会出现三种运动行为即翻越、回弹以及聚并.

Liquid marbles can be used as micro-droplet carriers due to their non-wetting,non-adhesion,and selective material exchange with the outside environment,wide applications in emerging fields like microfluidics and chemical,biological,and chemical microreactors.The collision can be used as a method of manipulating material transfer by marbles,which has significance and research value.Unlike droplet-droplet or marble-marble collisions,the collision behavior between marbles and droplets is more abundant and complex.The study of this process is vital for effectively transferring the material with marble as the medium.In this paper,high-speed camera filming technology is used to capture the collision process between liquid marbles and sessile droplets.The collision process between marbles and droplets is investigated for different Ohnesorge numbers(Oh)and wall hydrophilicity/hydrophobicity(contact angle:θ~35.4°-124.5°).This research demonstrates that at the hydrophilic interface,the contact angle formed between the droplet and the interface is small(q≤61.3°),and when the collision occurs,the effective contact area is small,which cannot form a larger obstruction to the forward motion of the marble and ends the collision with the droplet in the form of overturning;when the hydrophobic interface is changed into the hydrophobic interface,the effective collision area increases,which forms a larger obstruction to the forward motion of the marble and replaces overturning with rebound behavior;when the hydrophobicity of the interface increases to q=124.5°,the effective collision area becomes larger,and the fluctuations generated at the interface after the collision cause the particles on the surface of the marble to migrate and appear in the exposed area,forming a liquid bridge and then quickly completing the aggregation.When marbles and sessile droplets collide,three distinct motion behaviors emerge:climbing,rebound,and coalescence-merging(coalescence).