Fabrication and Properties of Poly(styrene)-block-Poly(hydroxyethyl methacrylate)/Eu Complex Honeycomb Structured Porous Films via Breath Figure Method

Amphiphilic copolymers, poly(styrene)-block-poly(hydroxyethyl methacrylate)/Eu complex (PS-bPHEMA/Eu complex) were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The structure and composition of the amphiphilic copolymers, PS-b-PHEMA/Eu complex, were characterized by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), H-1-nuclear magnetic resonance spectroscopy (H-1-NMR) and solid-state fluorescence spectrum. The honeycomb structured porous films were fabricated by dropping the PS-b-PHEMA/Eu complex copolymer solutions onto glass substrates via the breath figure method. The effects of solvent, copolymer concentration, and copolymers' molecular weight on the formation of porous films were investigated. The surface morphology and elemental mapping of the highly ordered porous films were investigated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and laser scanning confocal microscopy (LSCM). The results indicated that the solvent type, copolymer concentration, and copolymers' molecular weight can affect the surface morphology of the honeycomb structured porous films. Organic solvents with low boiling point, high volatility, and insolubility in water are conducive to the formation of porous films with high regularity and uniform pore size. The average diameter of the pores in the porous films decreased with the increasing polymer concentration and the molecular weight of the copolymers. The FESEM-EDX analysis further verified that the hydrophilic groups (Eu complex groups) were mainly distributed at the sidewall of the pore, which was consistent with the LSCM results. It is worth mentioning that after the porous films were placed in the air for half a year, most of the Eu elements originally concentrated in the inner wall of the pore migrated to the surface of the films. This might be due to the migration of hydrophilic groups attached on the polymer chains with free rotation of the chains.