Flow induced streamer formation in particle laden complex flows

We study the combined flow of a polyacrylamide (PAM)solution with polystyrene (PS) nanoparticles, through a microfluidic device containing an array of micropillars. The flow is characterized by a very low Reynolds number (\textit{Re\textless \textless 1}). We find that for exceeding a critical Weissenberg number (\textit{Wi}$\ge $ 20), PS nanoparticles localize near pillar walls to form thin slender string-like structures, which we call `streamers' due to their morphology. Post-formation, these streamers show significant viscous behavior for short observational time-scales, and at longer observational time scales elastic response dominates. Our abiotic streamers could provide a framework for understanding similar structures that often form in biological systems.