Thermo‐Responsive Jamming of Nanoparticle Dense Suspensions towards Macroscopic Liquid–Solid Switchable Materials

Nanoparticle aggregation for constructing functional materials has shown enormous advantages in various applications. Most efforts focused on ordered nanoparticle aggregation for specific functions but were often limited to irreversible aggregation processes due to the thermodynamic equilibrium. Herein, we report a reversible disordered aggregation of SiO 2 ‐PNIPAAm nanoparticles (SPNPs) through thermo‐responsive jamming, obtaining smart liquid–solid switchable materials. The smart materials can display a switch between liquid‐like state and solid‐like state responding to a temperature change. This unique macroscopic behavior originates from the reversible disordered aggregation modulated by temperature‐dependent hydrophobic interactions among the SPNPs. Notably, the materials at the solid‐like state show anti‐impact properties and can withstand the impact of a steel sphere with a speed of 328 cm s −1 . We envision that this finding offers inspiration to design smart liquid–solid switchable materials for impact protection.