Near-Zero Creep Ionic Elastomer for Non-drifting Ear Electroencephalogram Signal Acquisition

Monitoring and identification of ear electroencephalogram (Ear-EEG) signals offer a promising non-invasive approach for tracking mental states. Compared to rigid metal electrodes, polymer electrodes possess flexibility, good biocompatibility, superior skin adhesion, and wearing comfort, however, their accuracy is often compromised by signal drift due to polymer creep under sustained strain. To address this, we introduce a molecular strategy that suppresses creep by compensating entropy loss through a designed intramolecular dihedral structure. The copolymer integrates two distinct crosslinks: flexible segments stabilized by electrostatic self-coordination, and a minority of rigid segments formed by covalent main-chain bridges. In-situ scattering and theoretical simulations confirm that the covalently bridged TAO segments adopt a rigid dihedral configuration, effectively restraining chain slippage and eradicating viscoelasticity. Concurrently, dynamic disulfide exchange further enhances network stability under deformation. This design yields the near-zero creep polyelectrolyte ionic elastomer, denoted as Poly(TA-co-TAT)-TAO, which demonstrates remarkable stretchability (>200%) and elasticity (hysteresis <7.5%, recovery >99% at 160% strain). Leveraging its persistent creep resistance (<0.4% over 12 hours), the resulting wearable EEG device enables reliable, long-term mental status monitoring in real-world settings. Polymer electrodes are promising for wearable ear electroencephalogram sensors, though they are sensitive to polymer creep under sustained strain. Here the authors report a crosslinked copolymer which resists creep for stable sensing.