Supramolecular Networks with High Shear Stiffening Enabled by Metal Ion-Mediated Hydrogen Bonding Enhancement Strategy

Shear stiffening gel (SSG) with prominent rate-dependent mechanical properties has been gaining increasing attention as soft armor for protecting the human body and equipment. However, the current SSG focused on polyborosiloxane (PBS) is hampered by the corrosion and toxicity of boric acid. Therefore, we design the supramolecular dynamic reversible networks without boric acid using a metal-ion-mediated hydrogen bonding enhancement strategy. We synthesized a series of alkoxysilane-modified polydimethylsiloxane (PDMS), which could condense with titanates, forming the relatively stable Si-O-Ti bond. Different oxidation states of the Ti atom influence the charge distribution of the adjacent hydroxyl group (Ti-OH). Consequently, the electrostatic potential of the H-bond donor and acceptor could be effectively modulated by the Ti4+ and Ti3+ cations, respectively, thereby enhancing the H-bond strength. As a result, the dynamic reversible networks of polytitanosiloxane (PTS) exhibit an exceptional shear stiffening response of ~2800 times, transitioning from 0.1 to 100 Hz. Meanwhile, the PTS SSG exhibits negligible corrosion to steel and low cytotoxicity of Level 1. The PTS SSG is further explored for applications in impact protection materials and flexible mechanical sensors, demonstrating excellent performance in practice. The hydrogen bonding enhancement strategy also paves the way for developing dynamic reversible networks to fabricate next-generation smart materials.