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

Abstract

Liquid marbles can be employed as micro-droplet carriers due to their non-wetting, non-adhesion, and selective material exchange with the outside environment, widely engaged in emerging fields like microfluidics and chemical, biological, and chemical microreactors. The collision can be used as a manipulation method for material transfer by marbles, which has significance and research value. Different from 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 the effective transfer of material with marble as the medium. This paper used high-speed camera filming technology to capture the collision process between liquid marbles and sessile droplets. The collision process between marbles and droplets was investigated for different Ohnesorge numbers (<i>Oh</i>) and wall hydrophilicity/hydrophobicity (contact angle:<i>θ</i>~35.4°-124.5°). This research demonstrates that at the hydrophilic interface, the contact angle formed between the droplet and the interface is small (<i>θ</i>≤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 to 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 is increased to <i>θ</i>=124.5°, before and after the collision, the flow state of the marble (before impacting:<i>We</i>~1.2-11.0,<i>Re</i>~808-2130; after impacting:<i>We</i><1,<i>Re</i>≤200) and the droplet (after impacting:<i>We</i>~1.5-3.1, <i>Re</i>~666-960) then changes, the effective collision area is larger, and the fluctuations generated at the interface after the collision cause the particles on the surface of the marble to migrate and appear exposed area, forming 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).