A paradigm shift in morphological architecture of PEO-b-PFOMA semi-fluorinated block copolymer thin films upon facile solvent annealing

Abstract

A systematical study on the morphological transition of the micelle films of semi-fluorinated poly(ethylene oxide)-b-poly(1H,1H-dihydro perfluorooctyl methacrylate) (PEO-b-PFOMA) diblock copolymers was carried out upon perfluroalkanes (PF-5080) or α,α,α-trifluorotoluene (TFT) solvent annealing. Poorly ordered short cylindrical structures of the PEO5k-b-PFOMA21k micelle film underwent a phase inversion with PEO cores in the PFOMA continuous phase with a short period of PF-5080 solvent annealing. In contrast, the highly ordered morphology of PEO10k-b-PFOMA21k with PFOMA cores in the PEO continuous phase developed into cylindrical microdomains presumably via the fusion process. Prolonged annealing of the film transformed its morphology into inverted-spherical domains of PEO in the PFOMA continuous phase through long-range ordering by following the fission process. In order to find out a synthetic application of the morphology inversion strategy, an attempt was undertaken by adding a gold precursor to the PEO10k-b-PFOMA21k micelle solution, and as-cast thin films were prepared accordingly. Upon PF-5080 solvent annealing, the nanoparticles populated in self-assembled thin films resulted in inverted-spherical domains having gold nanoparticles populated in PEO cores surrounded by the PFOMA continuous phase. When the annealing solvent was changed to TFT, a highly ordered in-plane cylindrical morphology with respect to the substrate was achieved from the poorly ordered cylindrical microdomains of the PEO5k-b-PFOMA21k thin film, whereas an uneven cylindrical structure was produced from PEO10k-b-PFOMA21k.