Ultra-Stretchable LENR/PEDOT:PSS/CuSO ₄ Hydrogel for Self-Powered, High-Sensitivity Human–Computer Interaction Touchpads

Human–computer interaction (HCI) devices demand materials that are simultaneously flexible, conductive, and mechanically resilient. Here, we report an ultrastretchable and conductive hydrogel based on liquid epoxidized natural rubber (LENR), poly(acrylamide-co-acrylic acid), PEDOT:PSS, (labeled as LENR composite hydrogels) and CuSO4, engineered to deliver balanced electrical and mechanical performance for next-generation HCI systems. Spectroscopic and thermal analyses confirmed the formation of a robust hybrid network, with enhanced π–π interactions and increased hydroxyl content at optimal PEDOT:PSS loading. Among the synthesized hydrogels, the CuSO4-doped LENR/p(AAm-co-AA)/20%PEDOT:PSS (2b) formulation demonstrated the best balance of properties, achieving conductivity of 97.1 Ω–1·cm–1, resistivity of 0.0103 Ω·cm, capacitance of 37 ± 4 mF, and toughness of 2.20 × 109 J·m–3. The hydrogel also exhibited mechanoresponsive strain sensitivity with a gauge factor of ∼4.9 and >90% recovery after repeated deformation cycles. Comparative benchmarking confirmed that these values outperform or rival state-of-the-art conductive hydrogels, surpassing PEDOT:PSS/natural rubber (15–40 Ω–1·cm–1) and PEDOT:PSS/ionic liquid elastomers (∼80 Ω–1·cm–1), while approaching the capacitance of advanced in situ-functionalized PEDOT:PSS hydrogels (40–50 mF). The integration of the optimized hydrogel into a self-powered touchpad, utilizing carbonized Kapton electrodes and PET substrates, demonstrated reliable triboelectric charge generation and highly sensitive, reproducible touch responses. This study presents LENR/PEDOT:PSS/CuSO4 hydrogels as a sustainable and multifunctional platform for flexible, adaptive, and high-performance HCI technologies, with future potential for self-calibrating systems through machine learning-assisted signal optimization.