Tuning Electrokinetic Flow, Ionic Conductance, and Selectivity in a Solid-State Nanopore Modified with a pH-Responsive Polyelectrolyte Brush: A Molecular Theory Approach

Abstract

We use an efficient molecular theory approach to study electrokinetic flow within a pH-responsive nanopore grafted with a polyelectrolyte (PE) brush. The flow rate, migration and convective conductance, electric potential and velocity fields, species distributions and the degree of ionization of the weak PE functional groups and nanopore selectivity are obtained and interpreted while considering pH-induced surface charges. The theory is generally based on writing the overall free energy of the system including the entropies arising from the conformations of flexible, excluded volume chains, the mixing of mobile species, electrostatic contribution, and the free energy due to the chemical acid–base equilibrium reactions. We demonstrate how, by controlling the bulk salt concentration, pH, surface grafting density, and PE drag coefficient, the flow inside the pore can be controlled. Generally, the flow rate gets enhanced upon decreasing pH, but the effect of salt concentration is more complex. As long as the pH is small (large), the flow rate decreases (increases) by increasing the salt concentration, while a nonmonotonic trend is evident at moderate pH values. We find that, when the PE drag coefficient is high (low), the flow rate decreases (increases) by increasing surface grafting density. For intermediate drag coefficients, the flow rate varies nonmonotonically with surface grafting density. It is observed that the convective ionic conductance obeys almost the same trend as the flow rate. It is also illustrated that the mean degree of ionization of the polymer chains and the migration ionic conductance enhance on increasing the background salt concentration, whereas the opposite is true for nanopore selectivity. However, when very low salt concentration is accompanied by a high pH value, there is a minimum in the nanopore selectivity. The present approach allows investigation of the application of PE-coated nanopores as smart nanovalves.

Pushing the limits of nanopore transport performance by polymer functionalization

“…On the other hand, theoretical studies demonstrate the influence of polymer amount and charge density, polymer sequence, molecular weight, or polymer distribution on ionic transport, highlighting the relevance of polymerization control in nanopores. 14,135,[154][155][156][157][158] Experimentally, it has been demonstrated that polymer amount, and with this charge density in nanopores, and consequently ionic permselectivity can be gradually adjusted using different This journal is © The Royal Society of Chemistry 2022 polymerization reactions such as ATRP, RAFT, and iniferterinitiated reactions. 137 Clochard and colleagues adjusted the PAA filling degree of PVDF ion track etched pores with pore diameters below 50 nm.…”

Thermo-osmotic transport in nanochannels grafted with pH-responsive polyelectrolyte brushes modelled using augmented strong stretching theory

“…It considers that the brushes do two things: (1) they trigger a particular EDL distribution and hence a particular distribution of the EOS body force (and other possible forces related to the EDL) and (2) they impart an additional gross drag force (with drag coefficient varying quadratically with the monomer distribution) on the fluid flow. In this context, the natural question arises that why these other papers (Yeh et al 2012a,b,c;Benson et al 2013;Milne et al 2014;Zeng et al 2014Zeng et al , 2015; 917 A31-4 Poddar et al 2016;Zhou et al 2016;Zimmermann et al 2017;Sadeghi 2018;Sin & Kim 2018;Hsu et al 2019;Huang & Hsu 2019;Lin et al 2019;Reshadi & Saidi 2019;Sadeghi et al 2019Sadeghi et al , 2020aKhatibi et al 2020;Silkina et al 2020;Talebi et al 2021;Wu & Hsu 2021) did not witness such an increase in the electrokinetic transport in brush-grafted nanochannels as compared with that in brush-free nanochannels. First and foremost, none of these papers even attempted to compare the flow field in a brush-grafted nanochannel with that in a brush-free nanochannel under the condition where the net charge on the wall (for the case of brush-free nanochannel) is distributed on the brushes (for the case of brush-grafted nanochannel).…”

Scaling Behaviors of Nanoparticle Clusters That Are Driven through Brush-Decorated Nanopores

“…Nanofluidic systems designed on the basis of nanopores have received wide interest in recent decades due to their outstanding performance in new applications, , including material fabrication, − detection/sensing of macroparticles, − surface functionalization, − or the optimization of new nanomaterials. − One of the main goals in these applications is to enable the control of particles (e.g., DNA, − proteins, , or ions − ) which flow through the nanofluidic device. To achieve this function, the properties of fluids that can be manipulated by electromagnetic fields, , electrically charged or superhydrophobic nanopore surfaces, hydrogels, − and stimulus-responsive polymer brushes are employed.…”