Electrically Conductive Kevlar Fibers and Polymer-Matrix Composites Enabled by Atomic Layer Deposition

Multifunctional composites that incorporate nonstructural capabilities such as energy storage, self-healing, and structural health monitoring have the potential to transform load-bearing components in automotive and aerospace vehicles. Imparting electrical conductivity into polymer-matrix composites (PMCs) is an important step in enabling multifunctionality while maintaining mechanical stiffness and strength. In this work, electrically conductive PMCs were fabricated by conformally coating Kevlar 49 woven fabrics with aluminum-doped zinc oxide using atomic layer deposition (ALD). Electrical resistance was measured at the single-fiber, single-tow, and woven fabric levels as a function of coating thickness. The ALD coatings on adjacent fibers merge as their thickness increases, resulting in an interconnected network with improved percolation and lower resistance. After ALD, the fabrics were embedded in an epoxy matrix to manufacture PMCs. The electrical resistance of the composites increased with applied tensile strain, which was attributed to cracking of the conductive coatings. The relative change in resistance as a function of strain varied with coating thickness, which was rationalized by a thin-film fracture mechanics model. This work demonstrates a pathway for scalable and tunable incorporation of electrical conductivity into fiber-reinforced composites without significantly changing their density or load-bearing capabilities.