Interfacial Force-Focusing Effect in Mechanophore-Linked Nanocomposites

Enhanced force transmission to mechanophores is demonstrated in polymer nanocomposite materials. Spiropyran (SP) mechanophores that change color and fluorescence under mechanical stimuli are functionalized at the interface between SiO₂ nanoparticles and polymers. Successful mechanical activation of SP at the interface is confirmed in both solution and solid states. Compared with SP-linked in bulk polymers, interfacial activation induces greater conversion of SP to its colored merocyanine form and also significantly decreases the activation threshold under tension. Experimental observations are supported by finite element simulation of the interfacial stress state. The interfacial force-focusing strategy opens a new way to control the reactivity of mechanophores and also potentially indicates interfacial damage in composite materials.