Switchable nanochannel flow control through weak polyelectrolyte brushes

Surface modification of nanochannels with polyelectrolyte brushes (PEBs) offers a powerful mechanism for controlling nanoscale flow transport. In aqueous environments, weak polyelectrolytes (PEs) possess ionizable groups whose charges are influenced not only by pH and salt concentration but also by the conformations of PEBs and solvent flow. This charge-structure coupling is a key feature in nanofluidics, yet its effects on transport behavior remain poorly understood. We employ hybrid Monte Carlo/molecular dynamics simulations to model the dissociation/association of ionizable groups, combined with dissipative particle dynamics to simulate solvent flow. Our results reveal that nanochannels coated with weak PEs enable switchable control of pressure-driven flows, exhibiting an on–off transition between slow flow in a closed state and rapid flow in an open state, with the flux between the two states differing by almost one order of magnitude. Furthermore, compared to constant-charge strong PEBs, the on–off transition occurs at a lower pressure gradient for charge-regulating PEBs due to a dynamic reduction in degrees of ionization in response to brush compression under external flow fields. Our work offers novel microscopic insight into flow control within smart nanofluidic systems utilizing grafted weak PEBs and demonstrates an efficient and accurate numerical methodology to advance future studies on the non-equilibrium dynamics of pH-responsive soft materials under flow conditions.