Spatial Variations in Hydrogen Bonding Interaction within Polymer Blends Revealed by Infrared Nanoimaging

Hydrogen bonding plays a crucial role in enhancing the miscibility of polymer blends, allowing for the tailoring of their physicochemical properties to meet diverse application demands. However, nanoscale imaging of its impact on the phase-separation behavior of multicomponent polymeric materials remains largely unexplored. In this work, we introduce scattering-type scanning near-field optical microscopy (s-SNOM) equipped with a broadly tunable quantum cascade laser as a tool for investigating spatial variations in hydrogen-bonding interactions within blends of polyvinyl acetate (PVAc) and polyvinylphenol (PVPh), spin-coated from tetrahydrofuran solution. Our multiwavelength s-SNOM imaging approach reveals distinct features, namely, the hydrogen bonding mediated miscible PVAc/PVPh blend and the phase-separated PVAc domain. These results provide a more detailed understanding, indicating that hydrogen bonding may not lead to a completely uniform blend throughout the film, as previously believed, based on far-field spectroscopy. Furthermore, through comparisons between topography and near-field images, we find that the PVAc/PVPh hydrogen-bonded domain exhibits a strong affinity for the Si surface with its native oxide, while the free (non-hydrogen-bonded) PVAc film is vertically phase-separated atop the blend. Overall, our work demonstrates that s-SNOM is an effective and efficient tool for studying intermolecular interactions relevant to various chemical and biological phenomena.