Improved Elasticity and Conductivity in a Ni@Ag/Silicone Rubber Composite due to Lowered Percolation Threshold via Magnetic-Field-Induced Alignment

Abstract

Elastic and conductive electrodes are required for deformable electronic devices. The electrical conductivity and elasticity of a composite material are governed by the proportions of conductive filler and polymer matrix, respectively. Achieving these two features simultaneously is challenging because of the trade-offs between them. The conductive filler content must be higher than the percolation threshold to achieve conductivity. However, if the percolation threshold could be lowered, conductivity could be achieved even with a low content of the conductive filler, and elasticity could be achieved simultaneously by increasing the content of the polymer matrix. Herein, a Ni@Ag/silicone rubber composite with a decreased percolation threshold via magnetic field alignment is reported. The magnetic/conductive particles were arranged and compressed in a parallel straight-line pattern using an external magnetic field. The resulting pseudo-one-dimensional (1D) morphology lowered the percolation threshold of the composite by more than 20% and maintained its electrical properties at 20% cyclic stretching. However, composites that were oriented one way were only able to withstand stretching in a perpendicular direction. By creating a cross-directional orientation procedure, we were able to resolve this problem. In addition, factors affecting the conductivity and elasticity, such as the strength and direction of the magnetic force and the content of the multi-walled carbon nanotubes (MWCNTs), were studied. The MWCNTs served as the nonmagnetic conductive secondary filler, helped control viscosity, and improved the elasticity. Through an light-emitting diode (LED) demonstration, it was proved that the magnetic-field-induced alignment process can be applied to a circular electrode circuit for deformable electronics.