Gallium (Ga) has gained widespread recognition as a fascinating and distinct element on the periodic table. Research featuring Ga has been recognized by the American Chemical Society as one of the top stories in 2016 [1], while an article indicated that such materials are currently experiencing a revival [2]. Moreover, over the past decade, the literature has seen a dramatic surge in references to these materials, with an annual growth rate of approximately 21% [3].

Ga is categorized as a post-transition element and can be found directly beneath Aluminium (Al) on the periodic table, resulting in numerous parallels with Al, with the exception of one notable distinction – its melting temperature. The melting point of Ga is 29.8 °C, indicating its transformation into a liquid state on a warm day and its comparable bulk viscosity to water (viscosity of water and Ga are 1.0 × 10−3 Pa·s and 2.4 × 10−3 Pa·s, respectively, at 20 °C) [4,5]. The presence of both covalent and metallic bonding in solid Ga, explains its low melting point [6].

It is indeed remarkable that Ga has an vapour pressure < 10−6 Pa at 500 °C, whereas, conventional liquid metal (LM) such as mercury has a significantly higher vapour pressure of 0.1713 Pa at 20 °C (standard room temperature) [7]. This feature ensures safety during handling and eliminates concerns about inhalation. It's extremely low vapour pressure makes it suitable for use in high vacuum conditions, without the concern of evaporation [8]. Ga, like many other molten metals, exhibits the phenomenon of supercooling, which enables it to be cooled significantly below its melting point before solidifying. Additionally, LMs exhibit minimal solubility in majority of liquids [9], ensuring their compatibility with different fluids in a range of devices without any dissolution concerns [10].

Historically, LMs have been associated with toxicity, as exemplified by mercury. Furthermore, the earliest reported applications of Ga failed to achieve the desired level of manoeuvrability. An example of this can be seen in a 1954 Science publication where it was noted that “despite all precautions, this Ga electrode always behaved erratically,” [11] due to Ga’s high environmental reactivity. The reactivity of Ga causes the formation of a thin layer of native oxide (1–5 nm), which has an effect on its surface chemistry, wetting, and rheology. Finally, Ga may not be given the recognition it deserves due to its tendency to diffuse into the grain boundaries of select solid metals, such as Al [12], resulting in a significant degradation in mechanical properties [13].

It is only in recent times that scientists have started to uncover the intricate nature of Ga surface reactivity and utilize its potential for a diverse array of applications. Manipulation and control of LM and its interface can lead to a range of properties, including electrochemical, electromechanical, thermomechanical, catalytic, and biochemically responsive ones. Fig. 1 (a) showcases the different properties of liquid Ga leading to the various multi-disciplinary applications. While the literature is currently experiencing a tremendous surge of interest in the field of LM, the topic concerning the fundamental characteristics of LMs remains fragmented. Therefore, the primary objective of this review is to provide a comprehensive coverage of the fundamental aspects of Ga-based alloys that explain their resurgence. Furthermore, we present an overview of the state-of-the-art technological advancements in the field of LMs and direct readers to more specialized literature that underscores the significance of our work. In the text henceforth, the abbreviation “LM” is consistently utilized as most LMs containing Ga possess similar characteristics with a considerable level of accuracy [14].