Liquid marble and water droplet interactions and stability

Abstract

The interactions between two individual water droplets were investigated in air using a combination of coalescence rig and high speed video camera. This combination allows the visualization of droplet coalescence dynamics with millisecond resolution which provides information on droplet stability. Bare water droplets coalesced rapidly upon contact, while droplet stability was achieved by coating the droplets with polystyrene particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] hairs (PDEA-PS particles) to form liquid marbles. The asymmetric interaction of a water droplet (pH 3 or 10) armoured with the PDEA-PS particles (liquid marble) with a bare droplet at pH 3 exhibited intermediate stability with coalescence observed following an induction time. The induction time was longer for the pH 10 liquid marble, where the PDEA-PS particles have a hydrophobic surface, than in the case of a pH 3 liquid marble, where the PDEA-PS particles have a hydrophilic surface. Furthermore, film formation of PDEA-PS particles on the liquid marble surface with toluene vapour confirmed capsule formation which prevented coalescence with the neighbouring water droplet instead wetting the capsule upon contact within 3 milliseconds. This study illuminates the stability of individual particle-stabilized droplets and has potential impact on processes and formulations which involve their interaction.

The Potential of Liquid Marbles for Biomedical Applications: A Critical Review

“…In literature several works studying and exploring the ability of LM to float can be found – Figure A . Taking advantage from this LM property, applications were developed on sensors field for pH‐sensing, to reveal water pollution, and also on development of floating self‐propelling devices . Generally, pH‐sensing LM were coated with pH‐responsive particles that change their wettability from hydrophobic to hydrophilic with pH variations.…”

“…Widely range of applications were found for LM, such as oil adsorption and separation, pH and gas sensing, chemical reactions, synthesizing microparticles, revealing water pollution on the water/vapor interface and manipulation of small amounts of liquids (micro‐reactors, micro‐pumps) . The LM use in cosmetics has been also suggested, due to the non‐oily feel imparted to skin by marbles .…”

Stimuli‐Responsive Liquid Marbles: Controlling Structure, Shape, Stability, and Motion

“…Liquid marbles stabilized with polystyrene (PS) particles carrying poly[2‐(diethylamino)ethyl methacrylate] (PDEA) hairs were the first to be reported as stimuli‐responsive ( Figure ) . PDEA is a weak polybase with a p K a of 7.3 that is soluble in aqueous media below pH ∼7 because of protonation of its tertiary amine groups.…”

“…In particular, laser microscopy, confocal laser scanning microscopy, SEM and X‐ray computed tomography are powerful methods to characterize the surface roughness of the liquid marbles. It is expected that the combination of stereomicroscopy and optical microscopy techniques with high speed cameras will allow investigation of the dynamics of disruption, coalescence and motion of the liquid marbles induced by external stimuli at the millisecond timescale . The use of non‐volatile liquids, such as liquid metals, ionic liquids and liquid polymers, enables characterization by SEM and X‐ray photoelectron spectroscopy under high vacuum conditions.…”

Cell marbles: A novel cell encapsulation technology by wrapping cell suspension droplets using electrospun nanofibers for developmental engineering

“…Due to their several advantages, such as reduced amounts of reagents, shortened reaction rate, enhanced efficiency and flexibility, LMs have been proposed for various applications including gas and liquid sensing (Tian et al, 2010), microreactors (Arbatan et al, 2012), water pollution detection (Bormashenko and Musin, 2009) and medical applications (Avrămescu et al, 2018). There is also a growing interest to further improve their mechanical properties (Chin et al, 2013) or develop analogous systems with higher robustness (Ueno et al, 2015). In our previous research, electrospun nanofibres with engineered wetting properties and morphologies have been optimised and then used to encapsulate water and oil drops (Mele et al, 2014).…”