Hybrid Flexible Dry Electrodes for Electroencephalography: Electrical and Thermo-Mechanical Properties

This study evaluates styrene–ethylene–butylene–styrene (SEBS) composites modified with carbon nanotubes (CNTs) and carbon black (CB) for flexible electroencephalography (EEG) electrodes. Maleic anhydride-grafted SEBS (SEBS-MA) with 8 wt% CNTs and 2 wt% CB provides an optimal balance of conductivity and flexibility, a storage modulus comparable to SEBS, and yields a highly flexible conductive material. SEBS and SEBS-MA composites with 8 wt% CNT/2 wt% CB produced stable, low-noise signals, suggesting responsiveness to brain activity. The contact impedance of the elastomeric thermoplastic polymer (SEBS)/8 wt% CNT/2 wt% CB electrode is 4.25 ± 0.5 kΩ, and 4.5 ± 0.6 kΩ for SEBS-MA/8 wt% CNT/2 wt% CB, comparable to a commercial electrode (4.75 ± 1.5 kΩ). SEBS/8 wt% CNT/2 wt% CB and SEBS-MA/8 wt% CNT/2 wt% CB produced stable, low-noise EEG signals. In vivo EEG recordings demonstrated that SEBS-MA with 8 wt% CNT/2 wt% CB effectively captured transitions between the eyes-open and eyes-closed states, yielding clear and stable signals. These findings suggest that SEBS-MA/8 wt% CNT/2 wt% CB is a promising material for flexible, high-performance EEG electrodes due to its balance of electrical conductivity, mechanical stability, and signal clarity.