Liquid metals such as eutectic gallium indium alloy (EGaIn), due to their unique attributes such as voltage controlled surface tension, high liquid-state conductivity and liquid-solid phase transition at room temperature, open new avenues towards the development of programmable liquid materials.
Researchers at the University of Sussex and Swansea University, UK have exploited the self-locomotion, self-rotation, voltage controlled surface tension, high liquid-state conductivity and deformation characteristics of EGaIn and modulated its stiffness and density so that it would be possible to program the liquid metal in to a desired shape.
A liquid metal blob (certain quantity) in an electrolyte solution is highly conductive. In the absence of contact with any of the electrodes, external force and an applied voltage, the electrolyte induces a uniform charge distribution on the blob’s surface (Fig. 1(a)). However, when the blob is in contact with the anode (Fig. 1(b)) and a suitable voltage is applied to one or more of the other electrodes, the difference in the conductivity between the electrolyte and the liquid metal alters the charge distribution on the blob’ surface. The formation of an electric double-layer (EDL) at the blob’s interface enables deformation of liquid metal in the direction of the electric field (Fig. 1(b)). Hence, it would be possible to deform the liquid metal from anode (high voltage electrode) to cathode (low voltage electrode) to any desired shape (Fig. 1(c)).
Fig. 1 Influence of electric field on the deformation of liquid metal: (a) A liquid metal blob far from the electrodes and in absence of field is subject to no force; (b) Deformation of the blob upon contact with anode and an electric voltage is applied across it; and (c) Deformation of liquid metal to a desired shape.
The basic electrode array control algorithm to deform liquid metal in to a desired shape is shown in Fig. 2. In this system arrangement, the cathode attracts the liquid metal and the anode keeps the liquid metal in a wet and flat state (having the lowest surface tension). Hence, by switching only one selected electrode as cathode (low voltage) and setting all other electrodes as anodes (high voltage), the movement of liquid metal can be controlled. The relative voltage difference decides the speed of liquid metal deformation.
Fig. 2 Basic electrode array control algorithm to make alphabet letter “S”.
Three main problems that are inherent to liquid metal deformation still remains to be solved:
- H2 evolution at the cathode causes the liquid metal to branch out as multiple trees
- Higher surface tension of liquid metals at smaller size leads to splitting
- Liquid metal body interference stops its movement towards the cathode
The programmable liquid materials will find applications in soft robotics and shape changing, reconfigurable electronic circuits and display domains.
T.S.N. Sankara Narayanan
For a more detailed information, the reader may kindly refer: Yutaka Tokuda et al., Programmable Liquid Matter: 2D Shape Deformation of Highly Conductive Liquid Metals in a Dynamic Electric Field, Proceedings of the Interactive Surfaces and Spaces on ZZZ -ISS ’17 (2017). DOI: 10.1145/3132272.3134132
Recent Advancements in Science 