Mechanical Properties of Poly(dopamine)‐Coated Graphene Oxide and Poly(vinyl alcohol) Composite Fibers Coated with Reduced Graphene Oxide and Their Use for Piezoresistive Sensing

High‐strength poly(vinyl alcohol) (PVA) composite fibers are successfully fabricated through gel spinning, and reinforced by poly(dopamine)‐coated graphene oxide (dGO) and exterior reduced graphene oxide (rGO) coating. The mechanical properties of PVA/dGO composite fibers show a dependence on the sheet size of GO and interfacial adhesion force is formed by poly(dopamine) layers. The ultimate tensile strength and Young's modulus of PVA/dGO fibers are 1.58 and 27.2 GPa, and 68.1% and 97.1% higher than neat PVA fiber. In addition, there is an 8.2% and 21.4% increase relative to that of PVA/GO composite fiber. Moreover, exterior rGO layers are shown to reinforce the tensile strength of PVA/dGO composite fibers, and the tensile strength of rGO‐coated PVA/dGO composite fibers is 1.86 GPa. An adhesion force of poly(dopamine) between GO and the PVA matrix can efficiently transfer the tensile load via strong hydrogen bonding at interface, and exterior rGO layers can offer additional tensile strength through interfacial shear strength between rGO sheets. Additionally, a piezoresistive sensing test of rGO‐coated PVA/dGO fiber is shown that a gauge factor of 2.3 under 1% strain is achieved, leading to the potential use of this material in wearable strain gauges.