Materials with a temperature‐controlled reversible electrical transition between insulator and conductor are attracting huge attention due to their promising applications in many fields. However, most of them are intrinsically rigid and require complicated fabrication processes. Here, a highly stretchable (680% strain) liquid metal polymer composite as a reversible transitional insulator and conductor (TIC), which is accompanied with huge resistivity changes (more than 4 × 109 times) reversibly through a tuning temperature in a few seconds is introduced. When frozen, the insulated TIC becomes conductive and recovers after warming. Both the phase change of the liquid metal droplets and the rigidity change of the polymer contribute directly to transition between insulator and conductor. A simplified model is established to predict the expansion and connection of liquid metal droplets. Along with high stretchability, straightforward fabrication methods, rapid triggering time, large switching ratio, good repeatability, the TIC offers tremendous possibilities for numerous applications, like stretchable switches, semiconductors, temperature sensors, and resistive random‐access memory. Accordingly, a system that can display numbers and letters via converting alternative TIC temperature to a binary signal on a computer is conceived and demonstrated. The present discovery suggests a general strategy for fabricating and stimulating a stretchable transitional insulator and conductor based on liquid metal and allied polymers.

Stiffness tunable advanced materials have demonstrated their superiority and versatility in diverse areas, while the global pursuit of reversible, intelligent, and fast response for stiffness regulation is growing radically, leaving great challenges for traditional materials. As newly emerging functional metal material, the low melting point alloys (LMPAs) have shown encouraging potential in developing various stiffness regulation strategies owing to their excellent physicochemical and mechanical properties. This article is dedicated to presenting a comprehensive review of the LMPA‐enabled stiffness tunable materials from the aspects of material system, regulation principle and method, capability enabling mechanisms, and application scenarios. First, according to the structural differences, three kinds of LMPA‐enabled stiffness tunable material systems are evaluated. Then, the regulation strategies are elaborated from the fundamental LMPA modifications to dynamical external field controls, and the mainstream stiffness regulation modes are also combed out. Following that, the diversified applications of LMPA enabled stiffness tunable materials are systematically summarized and discussed. Finally, a perspective interpretation of the potentials and challenges of LMPA‐enabled stiffness tunable materials is provided. This article is expected to be important for guiding the future design of smart materials, functional entities, transformable robots, etc.

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As an emerging functional material, the liquid metal has demonstrated its encouraging potential in several areas with practical trials, while its global uniformity including high density and limited macroscopic interface might become a barrier for some tough application scenarios. Here, we proposed the concept of liquid metal foaming via decomposition agents, aiming to develop a generalized way to make porous foam metallic fluid, which would pave the way in achieving more structured features and adaptability of liquid metals. By introducing a greenness strategy with the help of an ecofriendly foaming agent, we realized a series of designed targeted liquid metal foams (LMFs). Compared with common liquid metals, LMFs possess many excellent properties, such as abundant interfaces, tunable conductivity, and adjustable stiffness, due to the controllable regulation of their porous structure. According to these unique characteristics, diversified values of LMFs were obtained. Benefiting from the naturally enriched interface in LMFs, the hydrogen evolution of LMFs in neutral deionized water was more efficient and more productive. Additionally, the compact LMF-air battery with high performance was originally manufactured. Moreover, the tunable LMF-enabled four-dimensional (4D) electromagnetic shielding materials possess excellent shielding performance. This material could open up broad vistas for the application of LMs.