Please do not remove this page
Liquid metal marbles
Sivan, Vijay Prasad; Tang, Shiyang; O'Mullane, Anthony; Petersen, Phred; Eshtiaghi, Nicky; Kalantar Zadeh,
Kourosh; Mitchell, Arnan
https://researchrepository.rmit.edu.au/discovery/delivery/61RMIT_INST:ResearchRepository/12246814770001341?l#13248370120001341
Sivan, Tang, S., O’Mullane, A., Petersen, P., Eshtiaghi, N., Kalantar Zadeh, K., & Mitchell, A. (2013). Liquid
metal marbles. Advanced Functional Materials, 23(2), 144–152. https://doi.org/10.1002/adfm.201200837
Published Version: https://doi.org/10.1002/adfm.201200837
Document Version: Accepted Manuscript
Downloaded On 2022/08/10 05:04:48 +1000
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Repository homepage: https://researchrepository.rmit.edu.au
Please do not remove this page
Thank you for downloading this document from the RMIT Research
Repository.
The RMIT Research Repository is an open access database showcasing the
research outputs of RMIT University researchers.
RMIT Research Repository: http://researchbank.rmit.edu.au/
Citation:
See this record in the RMIT Research Repository at:
Version:
Copyright Statement:
©
Link to Published Version:
PLEASE DO NOT REMOVE THIS PAGE
Sivan, V, Tang, S, O'Mullane, A, Petersen, P, Eshtiaghi, N, Kalantar Zadeh, K and
Mitchell, A 2013, 'Liquid metal marbles', Advanced Functional Materials, vol. 23, no.
2, pp. 144-152.
https://researchbank.rmit.edu.au/view/rmit:20460
A
ccepted Manuscript
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
http://dx.doi.org/10.1002/adfm.201200837
Submitted to
1
DOI: 10.1002/adfm
Liquid Metal Marbles
By V. Sivan, S. Y. Tang, A. P. O’Mullane, P. Petersen, N. Eshtiaghi, K. Kalantar-zadeh* and
A. Mitchell*
Dr. V. Sivan, Mr. S. Y. Tang and Assoc. Prof. K. Kalantar-zadeh*
School of Electrical and Computer Engineering, RMIT University, GPO Box 2476,
Melbourne VIC 3001 (Australia)
* kourosh.kalantar@rmit.edu.au
Dr. A. P. O’Mullane
School of Applied Science, RMIT University, GPO Box 2476, Melbourne VIC 3001
(Australia)
Mr. P. Petersen
School of Media and Communication, RMIT University, GPO Box 2476, Melbourne VIC
3001 (Australia)
Dr N. Eshtiaghi
School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476,
Melbourne VIC 3001 (Australia)
Prof. A. Mitchell**
Centre for Ultra-high bandwidth Devices for Optical Systems (CUDOS), School of Electrical
and Computer Engineering, RMIT University, GPO Box 2476, Melbourne VIC 3001
(Australia)
** arnan.mitchell@rmit.edu.au
Keywords: Liquid metal; liquid marble; galinstan; soft electronics; metal-semiconductor-
metal; electrochemical; heavy metal ion sensor.
We introduce "liquid metal marbles" which are droplets of liquid metal encapsulated by
micro– or nano–particles. We coat droplets of galinstan liquid metal with insulators (including
Teflon and silica), and also semiconductors (including WO
3
, TiO
2,
MoO
3
, In
2
O
3
and carbon
nanotubes) by rolling over a powder bed and also by submerging in colloidal suspensions. We
show that these marbles can be split and merged, can be suspended on water and are even
stable when moving under the force of gravity and impacting a flat solid surface. Further, we
show the marble coating can operate as an active electronic junction; and that the nano-
material coated liquid metal marble can act as a highly sensitive electrochemical based heavy
Submitted to
2
metal ion sensor. This new element thus represents a significant platform for the advancement
of research into soft electronics.
1. Introduction
The term ‘liquid marble’ was first introduced nearly a decade ago to describe droplets of
aqueous fluid encapsulated within hydrophobic particles.
[1]
These liquid marbles behave, to
some degree, like solid particles, but due to the fact that their structural form is dominated by
surface tension, they exhibit a number of unique properties, including very small contact area
with surfaces leading to low friction rolling, superhydrophobic interactions with other fluids
and the ability to be split or fused together with self-healing encapsulation layers.
[2]
Liquid
marbles rely on surface tension and can be formed with both non-polar or polar fluids
including water.
[1-5]
Indeed, water solutions encased with hydrophobic particles have great
potential for encapsulating biological environments even at nanolitre scales.
[6]
Due to the
unique capabilities of liquid marbles, there has been a large increase in the number of studies
on their properties as well as their practical applications.
[7-10]
Liquid metals have a long history of study in the fields of analytical chemistry, electronics,
and experimental physics. Traditionally, the most common liquid metal to be studied has been
mercury.
[11]
The toxicity of mercury however rendered applications based on this liquid metal
unattractive and thus research interest into the applications of liquid mercury has remained
niche. Recently, less hazardous liquid metals including eutectic alloys of gallium (75%) and
indium (25%) (eGaIn);
[12, 13]
and of gallium (68.5%), indium (21.5%) and tin (10%),
(Galinstan)
[11, 14, 15]
have become readily available and thus research interest in these
alternative liquid metals is gaining momentum. In general, liquid metals offer several unique
properties including high density (6440 kg/m
3
[11]
), high surface tension
Submitted to
3
(534.6 ± 10.7 mN/m
[14]
) and extremely low vapor pressure (< 10
−
6
Pa at 500ºC
[11]
) allowing
them to operate as liquids in vacuum conditions and high temperatures.
[11]
Most importantly,
liquid metals offer the highest conductivity of any liquids, with orders of magnitude less
conducting loss than ionic fluids making them attractive for various applications, such as in
soft electronic components,
[12, 13]
stretchable antennas,
[16-18]
interconnects,
[19, 20]
electromagnets,
[21]
MEMS switches
[22]
and reconfigurable wires.
[23]
Despite these many desirable properties, liquid metals share one major disadvantage for
practical use in that they are highly corrosive, particularly to other metals.
[24]
This means that
they will dissolve and amalgamate with solid contact metals such as gold which would be
typically used to electrically interface to the liquid metal to exploit its properties. Liquid
metals based on eutectic alloys of gallium in ambient air, forms a thin oxide layer which will
also adhere strongly to ionic surfaces such as glass
[11, 14, 25]
and even relatively low surface
energy polymers including polydimethylsiloxane (PDMS) which is often used to manipulate
fluids.
[22]
In order to effectively exploit the attractive properties of liquid metals, a means
must be found to prevent the fluid metal from adhering to its environment or corroding its
metal contacts, while maintaining both the flexible re-configurability offered by the fluid and
access to the electronic properties of the liquid metal.
In this paper, we present a novel approach to the use of liquid metals through the creation of
‘liquid metal marbles’. Here we encapsulate small droplets of galinstan within a coating of
nanoscale powders. We comprehensively studied the physical properties of such liquid metal
marbles in terms of their contact angle, splitting and fusing upon applying a force, floating on
aqueous media and dynamic properties during their free fall and impact on hydrophobic and
hydrophilic surfaces. We show that powders of nanoparticles can be used to achieve metal
liquid marbles with semiconducting properties at their surface. Achieving this, we
demonstrate several liquid metal marble properties including, the capability for forming
