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.

具有显著速率依赖性力学性能的剪切增稠凝胶（Shear stiffening gel, SSG）作为防护人体与装备的软质防护装甲，正受到日益广泛的关注。然而当前以聚硼硅氧烷（polyborosiloxane, PBS）为基材的SSG，却受制于硼酸所带来的腐蚀性与毒性问题。为此，我们采用金属离子介导的氢键增强策略，构建了不含硼酸的超分子动态可逆网络。我们合成了一系列烷氧基硅烷改性聚二甲基硅氧烷（alkoxysilane-modified polydimethylsiloxane, PDMS），该聚合物可与钛酸酯发生缩合反应，形成相对稳定的Si-O-Ti键。钛原子的不同氧化态会调控相邻羟基（Ti-OH）的电荷分布，据此，四价钛离子（Ti⁴+）与三价钛离子（Ti³+）可分别有效调控氢键供体与受体的静电势，进而提升氢键结合强度。最终，聚钛硅氧烷（polytitanosiloxane, PTS）的动态可逆网络展现出优异的剪切增稠响应：在0.1 Hz至100 Hz的频率区间内，其剪切增稠响应强度可达约2800倍。同时，该PTS基SSG对钢材表现出可忽略的腐蚀性，且具备1级低细胞毒性。我们进一步探索了PTS基SSG在冲击防护材料与柔性力学传感器中的应用，实际测试展现出优异的应用性能。本氢键增强策略也为开发动态可逆网络以制备下一代智能材料开辟了新的研究路径。