Investigating the degradation of the uniaxial rheology of polymers in the presence of dyes*

Extensional rheology is an important factor to determine the polymer behavior in various applications. Dye and polymer are used together in many industrial applications such as in inkjet printing, and food additives. However, despite the numerous applications of dye-polymer interactions, how dye affects the extensional rheology of polymers is still unclear. In this study, we investigated the effect of cationic Methylene Blue (MB) dye and anionic Fluorescein (Fl) dye on the extensional rheology of polyethylene oxide (PEO), xanthan gum (XG), and Boger fluids (BF). The capillary thinning dynamics of the dye-polymer solution was observed by the Dripping onto Substrate (DOS) method. The experimental results showed that the Fl dye had no effect on the inertio-capillary regime of PEO. However, in the elasto-capillary regime, the addition of Fl dye accelerated the pinch-off dynamics of PEO, causing a 40% and 50% reduction in the extensional viscosity, η_E and relaxation time, λ_E. Although adding Fl dye decreased the  η_E and  λ_E of the PEO, it had minimal effects on the η_E and  λ_E of XG and BF. On the other hand, η_E and  λ_E of PEO-MB dye solution did not change significantly (i.e., 10-20% decrease). However, in the presence of MB dye, the λ_E of XG decreased by 50% - indicating strong molecular interactions of the dye-polymer pairs when they are oppositely charged.