Templating effects in dye-containing polypyrrole-gelatin cryogels

Abstract

Polypyrrole-gelatin cryogels were prepared by cryopolymerization in the presence of safranin, methyl orange and Acid Blue 25 dyes. The macroporous morphology (pore size <55 μm) of the obtained materials was not affected by the introduction of the dyes. The used dyes are known to form templates and change polypyrrole morphology in similar polymerization conditions without gelatin. However, optical microscopy showed that the anionic dyes (Acid Blue 25 and methyl orange) did not precipitate and form morphology-guiding templates after addition of iron(III) chloride in the presence of gelatin. In contrast, the template-forming behavior of the cationic dye (safranin) was found to be preserved. Starting from 0.5 mol% of safranin (compared to the monomer) in the polymerization medium, the safranin templates were presumably incorporated into pore walls of the cryogels, reinforcing them, and increasing tensile modulus by ≈ 6 times (up to ≈400 kPa) compared to the cryogel without a dye. According to TGA, introduction of the dyes to the polypyrrole-gelatin aerogels resulted in decrease of their thermal stability. Molecular structure of the aerogels was studied by vibrational spectroscopy. The aerogel prepared in the presence of Acid Blue 25 had the highest conductivity (10.4 S cm−1) and specific surface area (37.5 m2 g−1) as well as porosity (95.1%) and pore volume (13 cm3 g−1). In general, incorporation of the dyes resulted in higher specific surface area (up to ≈10 times) of the materials, compared to the cryogels without a dye. Therefore, the preparation of polypyrrole-gelatin cryogels/aerogels in the presence of the dyes can be a promising approach for enhancement of their properties.