The effects of polydopamine coating on the electromechanical performance of polypyrrole/PET composite yarns

The development of durable and conductive coatings on polyethylene terephthalate (PET) yarns is critical for smart textiles but has remained limited by weak interfacial adhesion and coating uniformity. We introduced a Tris/N-Methyl-2-pyrrolidone (NMP) co-solvent (80:20 v/v) that controlled polydopamine (PDA) interlayer formation on hydrophobic PET and produced a smooth, chemically stable coating (∼139 nm within 10 h). Pure NMP does not support PDA polymerization, whereas Tris alone induces rapid aggregation and irregular deposits; the mixed solvent balances reaction rate and interfacial wetting, thereby enabling uniform PDA growth. Subsequent in-situ polymerization of polypyrrole (PPy) on PDA-modified PET produces compact, adherent coatings at oxidant-to-monomer molar ratio is 1:1. The optimized composite yarns exhibit a practical baseline resistance of 1.69 kΩ and improved electromechanical stability over 100 stretch-recovery cycles, with a resistance change (ΔR/R 0 ) of +102.1% compared with +225.8% for the PDA-free control (F0). This approach shortened PDA deposition time by > 50% relative to typical aqueous routes while enhancing interfacial robustness and cyclic durability. The co-solvent design provides a general pathway to fabric-compatible, reliable conductive yarns for wearable electronics and stretchable sensing.