Polymer Crystallization on Nanocurved Substrates: Distortion Versus Dewetting

The crystallization of a model semicrystalline polymer, namely, poly-3-hexylthiophene (P3HT), was studied as a function of the curvature at the nanometric scale and substrate surface free energy (SFE). Nanostructured substrates with a controlled local curvature were prepared by deposition of a 235 nm SiO2 particle monolayer, and their SFE was modulated by functionalization with octadecyltrichlorosilane, followed by radiofrequency plasma oxidation. The crystallization of ultrathin P3HT thin films, on the curved portions of the substrate, was found to mostly depend on the substrate SFE, while spontaneous wetting occurred in all cases. The effect is analyzed in terms of the interplay of polymer wetting (affecting the interfacial free energy) and lamellar crystallization, implying the modulation of crystallization enthalpy, demonstrating that the balance between SFE minimization and crystallization enthalpy maximization governs the phenomenon. The results highlight the role played by the surface nanostructuring in driving soft matter organization.