Particle Separation from Liquid Marbles by the Viscous Folding of Liquid Films

Abstract

Particle separation from fluid interfaces is one of the major challenges due to the large capillary energy associated with particle adsorption. Previous approaches rely on physicochemical modification or tuning the electrostatic action. Here, we show experimentally that particle separation can be achieved by fast dynamics of drop impact on soap films. When a droplet wrapped with particles (liquid marble) collides with a soap film, it undergoes bouncing and coalescence, stripping and viscous separation, or tunneling through the film. Despite the violence of splashing events, the process robustly yields the stripping in a tunable range. This viscous separation is supported by the transfer front of dynamic contact among the film, particle crust, and drop and can be well controlled in a deterministic manner by selectable impact parameters. By extensive experiments, together with thermodynamic analysis, we disclose that the separation thresholds depend on the energy competition between the kinetic energy, the increased surface energy, and the viscous dissipation. The mechanical cracking of the particle crust arises from the complex coupling between interfacial stress and viscous forces. This study is of potential benefit in soft matter research and also permits the study of a drop with colloid and surface chemistry.

Effect of particle size on the stripping dynamics during impact of liquid marbles onto a liquid film

“…Thus, this phenomenon shows that with LMs wrapped by larger particles it is more difficult to achieve particle separation, but the requirements for particle separation with different particle sizes can be obtained according to the two theoretical thresholds. Combined with the previous study, 36 the stripping regime can also be obtained for LM wrapping by Fe 3 O 4 powders in the range of E s + E f < E k < E f + E d . Thus, the theoretical thresholds based on the competition of energy are of potential benefit in particle separation research.…”

“…21,28 Furthermore, a free-standing soap film can realize the rapid and effective separation of particles from the liquid surface in a tunable range. 36 It is important to note that the desorption energies associated with particle separation depend directly on particle size, which is normally much higher than the thermal energy (kT). 37,38 However, the effect of particle size on particle separation has not been investigated so far, which this paper focuses on.…”

Preprogramming Floating Time of Liquid Marble

“…The liquid marble breaks in a stripping event. [ 43 ] The breakage starts from the bottom side of the liquid marble. In this breakage event, models of the liquid immersion inside the liquid marble shells are proposed.…”

Universality of Scaling Laws Governing Contact and Spreading Time Spans of Bouncing Liquid Marbles and its Physical Origin

“…[20][21][22]31 Our present paper is focused on universal laws describing bouncing liquid marbles on solid substrates. The impact of liquid marbles with soap films was studied in ref 24. Non-coalescence bouncing of liquid marbles on vibrated water bath was reported in ref 31.…”

“…Our work is devoted to the study of the bouncing of liquid marbles, first introduced in the pioneering paper by Quéré et al. − Liquid marbles (LMs) are droplets coated with colloidal particles enabling separation of the liquid within from the solid substrate by an air layer. − This separation gives rise to the high mobility of liquid marbles, thus representing an alternative to the lotus-like-inspired superhydrophobicity . Properties and applications of liquid marbles were studied intensively in the last decade. − Several biological applications of liquid marbles were reported. , In particular, the use of liquid marbles as microfluidic devices and micromixers was demonstrated. , Various techniques enabling fabrication of liquid marbles including noncontact and electrostatic manufacturing were described. , It should be mentioned that liquid marbles are separated from the solid substrate with air cushions, thus resembling the wetting regime inherent for superhydrophobic surfaces. − , Our present paper is focused on universal laws describing bouncing liquid marbles on solid substrates.…”