Honeycomb-patterned porous films fabricated via self-organization of Tb complex-loaded amphiphilic copolymers

Abstract

Amphiphilic copolymers, poly(styrene)-block-Tb complex (PS-b-Tb complex), were synthesized by reversible addition fragmentation chain transfer (RAFT) polymerization. The honeycomb structured porous films were fabricated via dropping the PS-b-Tb complex copolymer solutions on glass substrates by the breath figures method (BFM). The structure and composition of the amphiphilic copolymer PS-b-Tb complex were confirmed by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). 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 and copolymer concentration can affect the surface morphology of the porous films. The average diameter of the pores in the porous films decreased with the polymer concentration and the molecular weight of the copolymers increased. The FESEM-EDX analysis further verified that the hydrophilic groups (Tb complex groups) were mainly distributed at the pore wall, instead of at the outer surface layer of the films, which was consistent with the LSCM results.

Fig. 1. Schematic illustration for the formation of honeycomb porous films with PS-b-Tb complex by BFM.

Scheme 1. The synthetic routes of polystyrene (PS) and PS-b-Tb complex.

Fig. 2. The emission spectra of PS-b-Tb complex at excitation wavelength λ = 310 nm.

Fig. 3. Photographs (UV 365 nm) of the polymers solution, (a) photographs recorded under UV 365 nm for PS-b-Tb complex-2 of 6 mg mL⁻¹ solution at different solvent and PS was dissolved in dichloromethane at 6 mg mL⁻¹ solution, (b) photographs recorded under visible light of (a), (c) photographs recorded under UV 365 nm for PS-b-Tb complex of 6 mg mL⁻¹ solution in CH₂Cl₂ at different reaction time, (d) photographs recorded under UV 365 nm for PS-b-Tb complex-2 in CH₂Cl₂ at different concentrations.

Fig. 4. FESEM images of the porous films prepared from PS-b-Tb complex-2 solutions in CH₂Cl₂ at different concentrations (a) 2 mg mL⁻¹, D = 1.59 μm (b) 4 mg mL⁻¹, D = 1.38, (c and e) 6 mg mL⁻¹ at different magnifications, D = 1.13 μm and (d) 8 mg mL⁻¹, D = 1.18 μm, (f) correlation between pore size and solution concentration.

Fig. 5. FESEM images of the porous films prepared from 6 mg mL⁻¹ CH₂Cl₂ solution of PS-b-Tb complex, (a) PS-b-Tb complex-1, D = 1.55 μm, (b) PS-b-Tb complex-2, D = 1.50 μm (c) PS-b-Tb complex-3, D = 1.33 μm (d and e) PS-b-Tb complex-4 at different magnifications, D = 1.09 μm, (f) correlation between pore size and reaction time. Insets show water droplet profiles and contact angles.

Fig. 6. LSCM images of the porous films prepared from 6 mg mL⁻¹ CH₂Cl₂ solution of PS-b-Tb complex: fluorescence images of (a) PS-b-Tb complex-1, (b) PS-b-Tb complex-2, (c) PS-b-Tb complex-3, (d) PS-b-Tb complex-4; optical images of (a′) PS-b-Tb complex-1, (b′) PS-b-Tb complex-2, (c′) PS-b-Tb complex-3, (d′) PS-b-Tb complex-4.

Fig. 7. FESEM images of porous films generated from 6 mg mL⁻¹ solution of PS-b-Tb complex-2 in CH₂Cl₂, (a) EDX elemental mapping of Tb in porous films, (b) porous films of (a), (c) EDX elemental mapping of Tb in image (b), (d) EDX spectrum of (a) (the red spot in this figure represents the element Tb).