Interfacial phenomena of liquid marbles : compression, impact, and coalescence

Abstract

Liquid marbles are unique non-wetting droplets stabilized by micro- or nano-scaled solid particles in a gaseous environment. These particle-stabilized droplets act as tri-phase entities by providing microscale air-liquid-solid joint interfaces. Intriguingly, the compact particle layer renders liquid marbles non-wetting, low-sticky, and gas-permeable properties, enabling them to behave like soft solids that bare droplets cannot attain. Performing superior in acting as cargo for material delivery and microreactors for chemical and biological reactions, LM has attracted growing interest in its research community over the years. The stability of the liquid marble is crucial for its potential applications. Therefore, more understanding of their interfacial phenomena becomes critical.

This thesis studies the behaviors of liquid marbles under quasi-static compression, dynamic impact, and electrostatic-induced coalescence. Chapter 2 studies the particle distribution under quasi-static mechanical compression, which leads to the rupture of liquid marbles. Liquid marbles are consistently ruptured at the edge of the contact area between the marble and the compressing substrate. The particle density distribution is depicted with a proposed model. Chapter 3 discusses the impact of liquid marbles on solid surfaces; the marble stabilizes into a toroidal-shaped liquid cratering when the solid surface is rough. Chapter 4 investigates the coalescence of liquid marbles driven by electrostatics. Two liquid marbles coalesce when sufficient electric stress can overcome the restoring capillary pressure by charging embedded electrodes. In Chapter 5, liquid marbles can be stabilized into different arrested morphologies via divergent coalescence dynamics by varying the size of particles. The formation of arrested structures is attributed to the modulus of particle jamming layer balances the internal hydrostatic pressure difference.

In summary, this thesis covers several interfacial phenomena of liquid marbles. These intriguing phenomena expand our understanding of the interfacial properties of particle-stabilized interfaces and may optimize the intrinsic features of marbles for their application as micro-reactors.