Redefining Solvent Resistance: The Dominant Role of Solvent-Surface Interactions in Nanoconfined Polymers.

Polymer-based materials often suffer from poor solvent resistance, as polymers tend to swell, deform, and dissolve catastrophically when exposed to good solvents. Here, we demonstrate that infiltrating polymers in the interstices of densely packed nanoparticles can dramatically enhance their solvent resistance, even against good solvents. Surprisingly, we find that polymer removal is determined not solely determined by polymer-solvent interactions but also by underexplored solvent-nanoparticle interactions. Specifically, solvents that interact more strongly with the nanoparticle surface are more effective at displacing adsorbed polymer chains even when they are thermodynamically worse solvents for the polymer. This overlooked behavior arises from the interplay of polymer adsorption, confinement-induced entropy reduction, and solvent-surface affinity. By tuning nanoparticle surface chemistry, confinement scale, and polymer identity, we achieve PINFs that retain the polymer content even after prolonged exposure to aggressive solvents. These findings establish solvent-surface interactions as a key parameter for engineering robust polymer nanocomposites.