Liquid metals and their hybrids as stimulus–responsive smart materials

The re-emergence of room temperature liquid metals presents an exciting paradigm for an ideal combination of metallic and fluidic properties. The unique fluid metal features of non-hazardous Ga-based liquid metals, including high surface energy, low viscosity, electrical and thermal conductivity, a wide temperature range of the liquid state, and desirable chemical activity for many applications, have led to remarkable possibilities for harnessing their properties and achieving unique functionalities. The realization of their stimulus-responsivity and multi-functionality make Ga-based liquid metals an attractive family of ‘smart materials’ that could act as the basis of countless applications in new frontiers, covering a wide range from materials science and engineering to medicine. Constructing hybrids of Ga-based liquid metals with other functional materials can further extend the field-responsive capacity of liquid metals to incredible levels. An increasing number of reports have revealed Ga-based liquid metals and their hybrids as remarkable soft smart-response materials. Nevertheless, the mechanisms underlying their stimulus–response activities, their interactions with other functional entities, and efficient tuning in their intimate integration, still require further exploration. Considering the applications of Ga-based liquid metals and their hybrids, this review focuses on their field-responsive physical and chemical properties. The recent field-responsive reports are comprehensively presented. The analysis of their responsive properties and the types of field applied in each case are discussed, so that a critical outlook on this field can be established.