Fe3O4@SiO2/PAM/Glycerol photonic crystal film as a long-term effective sensor for ambient humidity

This photonic crystal film is prepared by combining magnetically responsive photonic crystals and photo-initiated polymerization of hydrogel films. Fe3O4@SiO2 superparamagnetic nanoparticles are dispersed in a glycerol aqueous solution containing monomer acrylamide, crosslinker N,N'-methylenebisacrylamide and photoinitiator 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone. Then it is followed by a photopolymerization reaction under a UV lamp and an external magnetic field simultaneously. The obtained Fe3O4@SiO2/PAM/Glycerol photonic crystal film shows brilliant structural color and the wavelength can shift from 436 nm to 652 nm as the ambient humidity changed from 11% to 93%. It is expected to realize humidity detection with the naked eye. The repetitive experiment shows that when the humidity response is repeated for 15 cycles, the RSD value of reflection wavelength at RH 11% and RH 93% are 0.79% and 0.74% respectively. Fe3O4@SiO2/PAM/Glycerol photonic crystal film can respond to ambient humidity at least for 60 days, indicating an excellent stability and accuracy.