Polymer Chain Conformation Triggers Electro-osmotic Flow in Uncharged Nanochannels

Electroosmotic flow (EOF) in nanoscale systems is traditionally associated with charged channel walls. Here, we report a new EOF mechanism in polyelectrolyte (PE) solutions confined within uncharged nanochannels, revealed by dissipative particle dynamics simulations. The flow is found to arise from a PE chain conformation-induced spanwise charge separation in the electric double layer (EDL). The flow exhibits vanishing velocity gradients on the channel wall, indicating a wall-dissipation-free transport of liquids. Comprehensive parametric studies are also performed to reveal the characteristics of the new EOF. Chain topology and stiffness critically regulate this conformation-induced EOF: increasing chain rigidity suppresses charge separation and reduces flow velocity, most prominently in linear chains and least in star-like chains. Long rigid chains adopt U-shaped or claw-like conformations under electric fields and channel confinement, reshaping charge separations and reducing the EOF velocity. Channel confinement further modulates flow characteristics, with PE distributions exhibiting different patterns for various chain topologies, evolving from single to double and even triple layers. The EOF velocity also exhibits a nonmonotonic variation with the decaying nanoconfinement due to oscillations of the charge separation in the EDL. For all topologies, the charge separation and the EOF are gradually suppressed due to screening effects of added salt. This work promotes the investigation of electroosmotic transport of complex fluids and offers insights for designing nanofluidic pumping systems based on molecular conformation.