Synergistic enhancement of the mechanical properties of polyurethane ionogel by halometallate ionic liquid-induced phase separation and hydrogen bond cross-linking

Abstract

Ionogels, an emerging and rapidly developing type of soft material, are widely employed in flexible electronic devices. However, the solvation effect induced by ionic liquids (ILs) causes increased fracture strain and reduced fracture strength in polymer matrices, and balancing this trade-off remains challenging. In this work, halometallate ILs were dispersed in a poly(urethane-urea) (PUU-AD) network using a swelling strategy to prepare high-strength (37.65 MPa) and high-toughness (153.30 MJ m⁻³) PUU-AD ionogels (PUU-AD/IL), with 67.6% and 76.2% higher strength and toughness than the pure PUU-AD elastomer, respectively. The enhanced mechanical properties of the PUU-AD/IL ionogels were attributed to the polymer-rich phase for dissipating energy effectively and the IL-rich phase for maintaining the network integrity during deformation. Meanwhile, the complex anions ([Zn_xBr_y]⁻) in halometallate ILs formed hydrogen bond cross-linking via C–H⋯Br and N–H⋯Br interactions, optimizing the distribution of hard domains in the polymer-rich phase and forming a more densely packed physical cross-linked network, thereby enhancing the overall structural stability. Furthermore, the PU ionogel sensors demonstrated a wide response range (maximum strain: 780%; maximum pressure: 1500 kPa) and rapid response/recovery time (177/236 ms), enabling real-time monitoring of human movement. This study provides a strategy for resolving the contradiction between stress and strain in PU ionogels.