Rheological and flow characteristics of extensible yield stress fluids

Many industrial fluids commonly used in 3D printing, food industries, and pharmaceutical applications are yield stress fluids with elastic nature (elastoviscoplastic fluids, EVP). The inherited elasticity of such fluids allows them to store energy, thus, they can partially recover after deformation and resist extension. Elastic effects have been shown to be responsible for phenomena such as the loss of fore-aft symmetry and the formation of a negative wake behind a spherical particle settling in EVP fluids, and the cusped shape of a bubble rising in EVP fluid. In practice, the extensional characteristics of EVP fluids are found to speed up the dispensing process when they are used as inks for 3D printing systems. However, there is a drawback of secondary droplets formation, after the breakup of the liquid filament, which may fall randomly and negatively affects the precision. Hence, tuning the elasticity of EVP materials and studying its effect in different flow scenarios is very important. To achieve a tunable extensional behaviour, we modify a well-studied EVP fluid (Pluronic F127 solution, PF127) by adding a high-polymer (poly ethylene oxide, PEO) at different concentrations. We report the effect of PEO addition on the shear and extensional rheology, as well as the flow behaviour of the modified materials.