Photo-controlled fabrication of honeycomb-patterned films in poly(N-vinylcarbazole/azobenzene) copolymer

• Highly ordered honeycomb-patterned polymer films were obtained by the help of UV illumination.
• A new type of copolymer comprising N-vinylcarbazole and azobenzene monomer was synthesized.
• The effect of UV illumination is interpreted by the photo-switched isomerization of the azobenzene component.
• Photo-switched isomerization from trans to cis-form increased the dipole moment of the copolymer.

We have obtained a highly ordered honeycomb-patterned porous film by the assistance of UV illumination on the fabrication of polymer solution by the breath figure process under humid conditions. For the photo-controlled fabrication, a new type of UV-sensitive polymer that comprises N-vinylcarbazole and azobenzene monomer, poly(N-vinycarbazole/4-[N′-(2-cyano-4-nitrophenyl)azo]-2,6-dimethylphenol methacrylate, was synthesized and fabricated without addition of an amphiphilic copolymer necessary to hold water droplets on the hydrophobic solution surface as an air-water interface stabilizer. Highly well-ordered regular structure of honeycomb-patterned films was obtained by the illumination of UV light during the fabrication. The effect of UV illumination on the fabrication of the polymer film can be interpreted by the photo-switched isomerization of the azobenzene component in the copolymer from trans- to cis-isomer, which increases the hydrophilicity of the polymer solution inducing the decrease of interfacial tension of the polymer solution for the formation of uniform honeycomb pattern.

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