Deformation and electrical properties of magnetic and vertically conductive composites with a chain-of-spheres structure

Vertically anisotropically conductive composites with aligned chain-of-spheres of 20–75 m m Ni particles in an elastomer matrix have been prepared by curing the mixture at 100°C–150°C under an applied magnetic field of ∼300–1000 Oe. The particles are coated with a ∼120 nm thick Au layer for enhanced electrical conductivity. The resultant vertically aligned but laterally isolated columns of conductive particles extend through the whole composite thickness and the end of the Ni columns protrude from the surface, contributing to enhanced electrical contact on the composite surface. The stress-strain curve on compressive deformation exhibits a nonlinear behavior with a rapidly increasing Young’s modulus with stress (or pressure). The electrical contact resistance R c decreases rapidly when the applied pressure is small and then more gradually after the applied pressure reaches 500 psi (∼3.4 MPa), corresponding to a 30% deformation. The directionally conductive elastomer composite material with metal pads and conductive electrodes on the substrate surface can be used as a convenient tactile shear sensor for applications involving artificial limbs, robotic devices, and other visual communication devices such as touch sensitive screens.