Two-photon microscopy as a visual tool for polymer compatibilization monitoring: the PE-EVOH case

In this study, we present two-photon microscopy (2PM) as an original technique to investigate the compatibilization between PE-HEMA and EVOH at the sub-micrometer level, both on the surface and in the bulk. 2PM is a nonlinear fluorescence imaging technique commonly exploited for thick biological tissue analysis. Here, we use 2PM to visualize polymer blending through 3D images of the obtained films. Compatibilization was performed in solution, upon functionalization of PE-HEMA with 1.4% molar of ODIN, a fluorescent molecule able to form multiple hydrogen bonds with EVOH and to act as a fluorescent probe. Different blends were synthesized, and the obtained films were analyzed by 2PM. For all compositions, it was demonstrated that ODIN is evenly distributed both on the surface and in the bulk. 2PM analysis of the thermally reprocessed specimen revealed that repeated reprocessing allows the reformation of ODIN dimers as the most stable H-bonding array in the solid state, partially reversing the compatibilization.