From Barrier at Water–Oil to Conduits at Ice–Oil: Ice-Crack-Enabled Chaperone Solvent Drives On-Demand Polymer Phase Transfer

Phase transfer of polymer nanoparticles (NPs) across immiscible liquids typically demands surface functionalization or mechanical agitation. Here, we demonstrate a proof-of-concept, modification-free transfer mechanism driven by a controlled freeze–thaw process. Using a hydrophobic perylene diimide (PDI) derivative (PDI-N-DAN) as a model, we show that freezing transforms the water–oil interface into an oil–ice interface threaded with temporary nanocracks. A chaperone solvent (2,2,2-trifluoroethanol, TFE) forms a directionally ordered layer within these conduits. This interfacial sleeve lowers the free-energy barrier, allowing lipophilic PDI-N-DAN NPs) to enter the cracks. Subsequently, as the ice melts, TFE templates solvent-shell reorganization, converting them into hydrophilic PDI-N-DAN NPs to yield stable water dispersions. Validated by systematic experiments and molecular dynamics simulation, this strategy repurposes ubiquitous ice defects to program interfacial chemistry, offering a reliable route for on-demand polymer phase transfer.