Liquid marbles: Physics and applications

Abstract

Liquid marbles are formed by encapsulating microscale volume of liquid in a particulate sheath. The marble thus formed is robust and resists rupture if the particulate layer covers the entire volume of liquid and prevents contact between the liquid and the substrate. Liquid marbles have been objects of study over the past decade. Research has been focused on understanding their formation and properties -both static and dynamic. A range of particulate materials as well as liquids have been employed to make these objects. This paper summarizes the state of the art in this regard and discusses new developments that are being discussed. Finally, some directions are proposed based on lacunae observed in the community's understanding -both in terms of the science as well as on the application front.

Liquid Marbles: From Industrial to Medical Applications

“…Liquid marbles behave as drops placed onto a hydrophobic surface. Thus, they display a high contact angle, minimum friction forces and can easily roll off the support [ 3 ]. The double solid-fluid character, explains these denomination of these formations, i.e., “liquid marbles”, “dry water”, “liquid pearls”.…”

“…Hydrophilic powders (graphene) [ 6 ], or even nanofibers made from fluoroalkyl and cellulose acetate co-polymers are also used as external phases, resulting in liquid marbles with superior structural properties compared to those with a hydrophobic powder shell [ 7 ]. The liquids used as an internal phase generally display high surface tension, therefore the global surface tension, responsible for the robustness of the liquid marble is also high [ 3 ].…”

“…A direct correlation between wettability of powders and liquid marbles formation was noticed. The literature shows that hydrophobic powders (both natural: Lycopodium , soot [ 8 ] and synthetic: polyvinylidene fluoride (PVDF), polytetrafluoro-ethylene (PTFE), polyethylene (PE) [ 9 ], polymethylmethacrylate (PMMA) [ 10 ], hydrophobic copper powder [ 11 ]) and also hydrophilic ones (graphene, carbon black) can be used to cover droplets [ 3 ].…”

An Electrostatic Method for Manufacturing Liquid Marbles and Particle-Stabilized Aggregates

“…The main difference was that our electrostatically-formed aggregate was a drop entirely filled with hydrophilic particles, whereas liquid marbles consist of a drop encased in hydrophobic particles. The resemblance was nonetheless of interest, since LMs display some remarkable properties, e.g., extreme recoverable deformability, low evaporation rate, and the ability to come into non-wetting contact with solid surfaces and to float on water (McHale and Newton, 2011 , 2015 ; Janardan et al, 2015 ). These properties have in turn inspired a range of proposed applications for LMs, including gas sensors (Tian et al, 2010 ), bioreactors (Arbatan et al, 2012a , b ), encapsulation media (Eshtiaghi et al, 2010 ; Ueno et al, 2014 ), pressure-sensitive adhesives (Fujii et al, 2016a ) and materials delivery carriers (Paven et al, 2016 ; Kawashima et al, 2017 ).…”

Natural and Artificial Superwettable Surfaces-Superficial Phenomena: An Extreme Wettability Scenario

“…Cases of hydrophilic particle-covered liquid marbles are possible due to air trapped between particles, resulting in aggregates which cover the droplets [80]. When discussing liquid marbles obtaining procedures, the most popular manufacturing method is the droplet rolling in a powder bed, as previously presented.…”