Post-transition elements, together with zinc-group metals and their alloys belong to an emerging class of materials with fascinating characteristics originating from their simultaneous metallic and liquid natures. These metals and alloys are characterised by having low melting points (i.e. between room temperature and 300 °C), making their liquid state accessible to practical applications in various fields of physical chemistry and synthesis. These materials can offer extraordinary capabilities in the synthesis of new materials, catalysis and can also enable novel applications including microfluidics, flexible electronics and drug delivery. However, surprisingly liquid metals have been somewhat neglected by the wider research community. In this review, we provide a comprehensive overview of the fundamentals underlying liquid metal research, including liquid metal synthesis, surface functionalisation and liquid metal enabled chemistry. Furthermore, we discuss phenomena that warrant further investigations in relevant fields and outline how liquid metals can contribute to exciting future applications.

This review discusses the opportunities provided by gallium liquid metal alloys for making various microfluidic components.

Significance: The utilization of small-scale pumps is presently hampered by their limited flow rates with respect to the input power or their rather complicated fabrication process. These issues arise as many conventional pumping effects rely on moving elements. Here, we demonstrate the concept of a liquid metal enabled pump with no mechanical parts by simply incorporating droplets of Galinstan. The liquid metal enabled pump creates high flow rates (>5,000 µL/min) at exceptionally low powers (<15 mW) by electrowetting/deelectrowetting the surface upon application of electric field. The presented pump is both efficient and simple; hence, it has the potential to advance the field of actuation in small-scale systems.

Controlled actuation of soft objects with functional surfaces in aqueous environments presents opportunities for liquid phase electronics, novel assembled super-structures and unusual mechanical properties. We show the extraordinary electrochemically induced actuation of liquid metal droplets coated with nanoparticles, so-called “liquid metal marbles”. We demonstrate that nanoparticle coatings of these marbles offer an extra dimension for affecting the bipolar electrochemically induced actuation. The nanoparticles can readily migrate along the surface of liquid metals, upon the application of electric fields, altering the capacitive behaviour and surface tension in a highly asymmetric fashion. Surprising actuation behaviours are observed illustrating that nanoparticle coatings can have a strong effect on the movement of these marbles. This significant novel phenomenon, combined with unique properties of liquid metal marbles, represents an exciting platform for enabling diverse applications that cannot be achieved using rigid metal beads.