Changes in morphology and optical properties of polyvinyl alcohol foils induced by Congo red dye concentration and stretching degree

To establish correlations between the optical and morphological properties of anisotropic polyvinyl alcohol (PVA) foils containing Congo red (CR) dye in various concentrations, characteristics such as degree of crystallinity, dichroic ratio, order parameter, birefringence, surface morphology, and three-dimensional texture parameters were estimated before and after stretching. An increase in morphological and optical anisotropy with the degree of stretching has been evidenced for both pure and CR-containing PVA foils, this behavior being facilitated by the presence of the dye. The study of these properties lays the foundation for understanding the circumstances in which PVA foils containing CR can be used as polarizing filters.