Year

2018

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

The re-emergence of room temperature liquid metals presents a forgotten exciting paradigm for an ideal combination of metallic and fluidic properties. The very unique fluid metal features of non-hazardous Ga-based liquid metals, including high surface energy, low viscosity, unlimited malleability, a wide temperature range of the liquid state, and desirable chemical activity for many applications, have been leading to remarkable possibilities and potentials for harnessing their properties and functionalities. The realization of stimulus-responsivity and multi-functionality makes Ga-based liquid metals a new family of “smart materials” – be regarded as the basis of multitudinous applications in frontiers covering from material science to engineering and medicine. Constructing hybrids of Ga-based liquid metals with other functional materials or groups can further extend this field-responsive capacity to incredible levels. An increasing number of reports on liquid metals have been published and revealed the abilities or activities of Ga-based liquid metals, as well as their alloys and constructed hybrids, as soft smart-response materials. However, development and systematic study of novel stimulus-responsive properties and the related unexplored application are still highly lacking.

Three different stimulus-responsive behaviors and the corresponding potential application with liquid metal-based nanodroplets and hybrids were studied in this doctoral thesis. For the first work, we reported a green and facile synthesis of the liquid metal nanoparticle by sonication liquid bulk sample in a thiol solution, which can be used as printing inks. Each liquid metal particle in the ink was protected by the oxide layer, which can be broken by external pressure. By using these liquid metal nanoparticle based inks, stretchable and flexible electronic devices have been fabricated and demonstrated on polydimethylsiloxane and polyethylene terephthalate plastic substrate by direct printing and laser etching. A continues and conductive thin film and path with defined micro- or nano-size can be obtained by applying localized pressure on the LM particles.

For the second work, we further investigated the temperature dependence electric and magnetic properties of the liquid metal constructed electronics. It was found that, below 6.6 K, the as-prepared liquid metal-based conductive electronics were superconductive and diamagnetic. A series of Ga-based liquid metals and corresponding nanodroplets, thus, have been developed to fabricate flexible superconducting micro/nanoelectronics by direct printing. Those nanoparticles retain their bulk superconducting properties and can be dispersed and stored in various solvents, including ethanol, acetone, and water. By using these dispersions as inks, stretchable and flexible superconductive devices, including microsize superconducting coils, electric circuits, and superconducting electrodes, have been fabricated and demonstrated on the substrate by direct handwriting, inject printing and laser engraving.

Based on the first two works, it can be found that the Ga-based liquid metals and their nanoparticles are ideal conductive materials for building flexible electronics. Nevertheless, simply developing soft conductive matter is not the panacea for all the mechanical-mismatch induced challenges in electronics, especially for biosystems that displaying highly diverse combinations of mechanical properties. To smartly match the mechanical features of the targeted specific area, we developed liquid metal-based magnetoactive slurries by dispersing ferromagnetic particles in a Ga-based liquid metal matrix. Besides the benefits from the combination of conductivity and deformability, the stiffness and viscosity of the materials system designed here can be reversibly altered and subtly controlled within a very short time and over a wide range in response to the magnetic field applied.

In summary, these demonstrated Ga-based liquid metals and their hybrids make the Ga-based liquid metals promising to build multi-functional electronics for the varying field with different requirements, as a smart electric system which can be controlled by the external field applied.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.