Flexible Dry Electrodes Based on Styrene-Ethylene-Butylene-Styrene/Carbon Black and Ethylene-Vinyl Acetate/Carbon Black for Electroencephalography: Electrical, Thermal and Mechanical Properties

Electroencephalography (EEG) is an essential technique for monitoring brain electrical activity in clinical, sports, and wearable health settings. However, traditional wet electrodes face issues like gel drying and skin irritation, while coated dry electrodes tend to degrade over time, affecting long-term signal stability. This study explores flexible dry electrodes made from conductive polymer composites—poly(styrene-b-ethylene-ran-butylene-b-styrene) filled with carbon black (SEBS/CB) and ethylene-vinyl acetate filled with carbon black (EVA/CB)—as affordable and recyclable alternatives to standard materials such as PDMS and TPU. The electrodes were manufactured using solvent casting and compression molding, ensuring even filler distribution and consistent surface quality. Both composites reached an electrical conductivity of around 0.01 S/m with a percolation threshold close to 12 wt% CB. Contact impedance tests showed better performance for SEBS/CB electrodes (5.4 ± 0.9 kΩ) compared to EVA/CB (26.7 ± 4.4 kΩ), nearing the value of a commercial flexible electrode (4.2 ± 0.5 kΩ). Mechanical testing confirmed that SEBS/CB is softer and more elastic, facilitating stable, low-noise EEG signal collection. Overall, SEBS/CB composites provide a good balance of electrical performance, flexibility, and scalability, highlighting their potential for next-generation, long-term EEG monitoring systems.