Polycaprolactone-based block copolymers for nanopatterning oxide materials via sequential infiltration synthesis

Sequential infiltration synthesis (SIS) has emerged as a powerful technique to integrate inorganic materials into polymeric templates for fabricating functional hybrid and inorganic-only nanostructures. While several polymers, including self-assembled block copolymers (BCPs), have been widely used as templates for inorganic and hybrid oxide nanostructures, biocompatible polymers such as polycaprolactone (PCL) have not been explored for nanopatterning. In this work, we investigate SIS in polystyrene-block-polycaprolactone (PS-b-PCL) BCPs to demonstrate the feasibility of PCL as a guiding polymer for selective infiltration of Al₂O₃. Fourier transform infrared (FTIR) spectroscopy confirmed the strong interaction of TMA-H₂O precursors with the oxygen-containing functional groups of PCL, while scanning electron microscopy (SEM) revealed well-defined Al₂O₃nanostructures after SIS and polymer removal. By varying the number of SIS cycles and processing temperatures, we observed systematic changes in the inorganic content and nanostructural fidelity, highlighting the tunability of the process. Notably, significant Al₂O₃incorporation occurred during the first SIS cycle due to strong PCL-precursor interactions, even at temperatures as low as 60 °C, making the process relatively low-resource and efficient. These findings demonstrate that PCL is a promising guiding polymer for SIS, with potential to extend beyond conventional polymers such as polymethylmethacrylate. This work opens new opportunities for fabricating oxide nanostructures with applications in nanopatterning, dielectric layer, and bio-related nanomaterials.