Study on the novel rare-earth nanocrystals/PNIPAM complex hydrogels prepared by surface-initiated living radical polymerization

A series of novel rare-earth nanocrystals/PNIPAM complex hydrogels were prepared by surface-initiated living radical polymerization with different contents of NaYF4:Eu3+ nanocrystals. The microstructure and performance of the NaYF4:Eu3+ nanocrystals and the complex hydrogels were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential scanning calorimetry (DSC) and photoluminescence (PL). The thermosensitive fluorescence behaviors of the complex hydrogels and the mechanisms were investigated. The results suggested that the nanocrystals were incorporated into PNIPAM gels with covalent bonding and the fluorescence performance of complex hydrogels was influenced greatly by either the ambient temperature or the content of nanocrystals. The PL intensity of the complex hydrogels increased with increasing temperature. The higher content of nanocrystals in the complex hydrogels, the sharper the transitions of volume phase variation around low critical solution temperature (LCST).