In situ temperature sensing with fluorescent chitosan-coated PNIPAAm/alginate beads

The interest in the development of non-contact temperature sensors for particle image velocimetry (PIV) is continuously growing. The integration of thermochromic tracers in PIV represents a critical step forward in experimental fluid mechanics, which would enable detailed full-field analysis of thermal and environmental flows. In this paper, interpenetrated polymer networks (IPN) PNIPAAm/alginate loaded with Nile Red (NR) fluorescent dye are used to develop beads for simultaneous non-contact temperature sensing and flow tracing in fluids. The novel IPN beads are coated with chitosan to properly modulate particle permeability in water. The thermochromic response of the fluorescent tracers is studied through fluorescence spectroscopy, evidencing an increase in the NR fluorescence emission up to twenty times above the lower critical solution temperature of PNIPAAm. These findings confirm the potential of fluorescent chitosan-coated PNIPAAm/alginate beads for in situ temperature in PIV.