Soft liquid-metal/elastomer foam with compression-adjustable thermal conductivity and electromagnetic interference shielding

With the development of 5G wireless technology and Internet of Things, electromagnetic interference (EMI) and heat generation in electronic devices and interconnects are becoming increasingly ubiquitous due to the proliferation of wearable electronics. It raises great concerns that EMI and elevated heat degrade device performance and also cause detrimental effects on human health. The soft and deformable materials that are capable of simultaneously shielding EMI and dissipating heat effectively are thus in high demand. Herein, a flexible composite material exhibiting substantial increases of electrical/thermal conductivities and EMI shielding effectiveness (SE) under compression was developed by introducing three-dimensional (3D) liquid metal (LM) network into an elastomer foam. The electrical conductivity, thermal conductivity, and EMI SE of the 3D LM/elastomer foam increase more than 14, 8.3, and 1.8 times, respectively, when compressed to a strain of 60% due to the compress-induced improvement in percolation of the LM. Moreover, neither microstructure damage nor performance degradation was observed in the foam during 10,000 compress-release cycles under 50% strain. Furthermore, we have demonstrated the proof-of-concept applications of the 3D LM/elastomer foam used as soft EMI shields and heat spreaders in wearable electronics.