Synergistic Surfactant-Assisted Sand-Milling Exfoliation of Graphene toward Highly Conductive Graphene/Cotton Yarns for Wearable Joule Heating

Scalable fabrication of highly conductive and flexible yarns is essential for next-generation wearable heating textiles. However, liquid-phase exfoliation of graphite into graphene remains constrained by the intrinsic trade-off between achievable concentration and quality of graphene dispersions. Herein, a simple and cost-effective sand-milling exfoliation strategy is developed for the large-scale production of graphene dispersions by exploiting the noncovalent surface interactions between graphene and a sodium dodecyl benzenesulfonate (SDBS)-carboxymethyl cellulose (CMC) bicomponent surfactant system. The bicomponent surfactant system not only lowers the surface tension of water to facilitate efficient exfoliation but also provides synergistic steric–electrostatic stabilization of graphene nanosheets. Through systematic regulation of the CMC molecular weight, stable graphene dispersions with a high concentration of up to ∼20 mg·mL–1 were obtained. The resulting graphene nanosheets exhibit a high proportion of few-layer structures (42%, ≤3 nm), uniform lateral dimensions of 0.6–0.8 μm, a low defect density (ID/IG ≈ 0.10), and an electrical conductivity of 7220 S·m–1. Benefiting from strong hydrogen-bonding interactions, graphene is uniformly deposited onto cotton yarns, resulting in flexible conductive yarns with a low resistance of 32 ± 19 Ω for a length of 2 cm and efficient Joule heating up to 130.6 °C at 5 V, demonstrating promising potential for wearable electronics. It is observed that hydrogen-bonding interactions play a dominant role in the graphene–cellulose interfacial interaction, enabling intimate interfacial contact and uniform graphene anchoring on the yarn surface. This interfacial coupling facilitates the formation of continuous conductive pathways, thereby accounting for the low electrical resistance and efficient Joule heating performance.