Magnetic and fluorescence properties of cobalt implanted hydrogels

Co-doped plain gels (PAAm) were prepared with and without pyranine fluoroprobe (8-hydroxypyrene-1, 3,6-trisulfonic acid, trisodium salt; POH), which have a OH- reactive group and three SO^-₃ ionic groups. Magnetization and fluorescence measurements were used for characterization of the gels. It was observed that both the plain gel itself and the gel including only POH (PAAm-POH) have a diamagnetic response to the external field. When the gels were synthesized together with cobalt (PAAm-Co) and cobalt/POH (PAAm-Co-POH), both gels magnetized in the direction of the magnetic field, as expected. However, the magnitude of the magnetization was different in the gels which were synthesized in the presence of POH and the one into which POH molecules were diffused after the synthesis, even though they have the same cobalt concentration. Fluorescence measurements and SEM micrographs were used to understand this surprising difference in the magnetization of PAAm-Co-POH gels. It was proposed that the electrostatic interaction between SO^-₃ groups of POH and free electrons of cobalt (Co⁺²) atoms led to the formation of Co-POH clusters having fewer unpaired electrons, and this results in a decrease in overall magnetization. It was also observed from the SEM images that the size of clusters depends on the Co-POH composition.