Stretchable nanoparticle conductors with self-organized conductive pathways

Abstract

Research in stretchable conductors is fuelled by diverse technological needs. Flexible electronics, neuroprosthetic and cardiostimulating implants, soft robotics and other curvilinear systems require materials with high conductivity over a tensile strain of 100 per cent (refs 1, 2, 3). Furthermore, implantable devices or stretchable displays⁴ need materials with conductivities a thousand times higher while retaining a strain of 100 per cent. However, the molecular mechanisms that operate during material deformation and stiffening make stretchability and conductivity fundamentally difficult properties to combine. The macroscale stretching of solids elongates chemical bonds, leading to the reduced overlap and delocalization of electronic orbitals⁵. This conductivity–stretchability dilemma can be exemplified by liquid metals, in which conduction pathways are retained on large deformation but weak interatomic bonds lead to compromised strength. The best-known stretchable conductors use polymer matrices containing percolated networks of high-aspect-ratio nanometre-scale tubes or nanowires to address this dilemma to some extent^{6,7,8,9,10,11}. Further improvements have been achieved by using fillers (the conductive component) with increased aspect ratio, of all-metallic composition¹², or with specific alignment (the way the fillers are arranged in the matrix)^13,14. However, the synthesis and separation of high-aspect-ratio fillers is challenging, stiffness increases with the volume content of metallic filler, and anisotropy increases with alignment¹⁵. Pre-strained substrates^{16,<a id="ref-link-abstract-17" title="Xu, F., Wang, X., Zhu, Y. T. & Zhu, Y. Wavy ribbons of carbon nanotubes for stretchable conductors. Adv....}