Preparation and characterization of PVA/Congo red polymeric composite films for a wide scale laser filters

A PVA/Congo red composite film was prepared via casting technique. The effects of different concentrations of Congo red (CR) on the crystal structure and optical properties of polyvinyl alcohol (PVA) were characterized by X-ray diffraction and UV–vis spectroscopy. The PVA/CR films at different concentrations of CR displayed a relatively sharp peak at 2theta =19.51° and an additional weak broad peak corresponding to (200) plane of PVA at 2theta=22.35°. The transmittance values of PVA in UV–VIS above 600 nm were higher than PVA/CR films. Moreover, the transmittance of PVA/CR composite film decreased with the increase of CR dopant concentrations onto the PVA matrix; this could be attributed to the intermolecular hydrogen bonding between the hydroxyl group in PVA chains and the outer site groups (amino and sulfonate groups) in CR. Moreover, PVA/CR film (at 0.1 wt% CR) showed the properties of a broad scale cutoff filter in the UV–VIS range (190–566 nm).