Mobility Control of Mechanical Bonds to Modulate Energy Dissipation in Mechanically Interlocked Networks.

Mechanically interlocked networks (MINs) with dense mechanical bonds can amplify the dynamic behaviors of the mechanical bonds to exhibit decent mechanical properties. Energy dissipation resulting from mechanical bond motion is essential for improving toughness, yet effective strategies to optimize this process remain underexplored. Here, by designing mechanical bond models with controllable mobility, we establish a fortification strategy for the two key factors governing energy dissipation, host-guest recognition and sliding friction, thereby enabling mechanical property enhancement of mechanically interlocked materials. Specifically, the [2]rotaxanes in MIN- and MIN- exhibit identical axle structures, with MIN- incorporating a small benzo-21-crown-7 ring and MIN- incorporating a large benzo-24-crown-8 ring. Strain rate-dependent cyclic tensile tests reveal that the energy required to drive mechanical bond motion in MIN- and MIN- is 510 and 260 kJ/m, respectively, indicating that the small wheel size enhances host-guest recognition. Furthermore, the apparent activation energy for the sliding motion of the mechanical bonds in MIN- (11.0 kJ/mol) is higher than that in MIN- (6.70 kJ/mol), suggesting increased sliding friction in MIN-. Due to these two aspects, MIN- exhibits superior energy dissipation performance (damping capacity = 92%) compared to MIN- (78%), translating to a higher toughness (7.50 vs 5.70 MJ/m).