Processing-Dependent Interfacial Conformation of Adsorbed Polymers Induces Divergent Equilibration in Chemically Identical Polymer Nanocomposites

Polymer nanocomposites (PNCs) are recognized for their enhanced mechanical, thermal, and functional properties, but their behavior is not always dictated by chemistry. Instead, the interplay between processing history and interfacial chain properties can determine whether such systems reach equilibrium or remain trapped in long-lived metastable states. Here we show that compositionally identical PNCs, prepared by selectively preadsorbing either short or long polyethylene glycol chains onto silica nanoparticles, evolve toward fundamentally distinct structural and mechanical states during thermal annealing. While short-chain preadsorbed systems remain kinetically arrested, long-chain preadsorbed systems undergo dramatic interfacial reorganization, as reflected by exponential increases in the lowest-wavevector structure factor and the shear modulus. We reveal unusually high activation barri…