Antielectrophoretic Response-Driven Bending–Tilting Deformation of Cationic Polyelectrolyte Brushes Drives Nonlinear Electroosmotic Transport in Brush-Grafted Nanochannels

Journal Article · Thu Feb 27 00:00:00 EST 2025 · ACS Applied Polymer Materials

DOI:https://doi.org/10.1021/acsapm.4c03266· OSTI ID:2568483

Ishraaq, Raashiq ^[1]; Das, Siddhartha ^[1]

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1. University of Maryland, College Park, MD (United States)

In this paper, we use all-atom molecular dynamics (MD) simulations to describe a non-linearly enhanced electroosmotic (EOS) flow, where, in a nanochannel grafted with cationic PMETAC ([Poly(2-(Methacryloyloxy)Ethyl) Trimethylammonium Chloride]) brushes, a two-fold increase in the electric field strength leads to a several-fold (more than two-fold) increase in the EOS flow strength and volume flow rate. The electric field enforces the PMETAC brushes to undergo a bending-tilting driven deformation with a significant portion of the brush layer becoming parallel to the grafting surface. In response, a substantial fraction of the counterions leave the brush layer (hence become more mobile), but instead of going into the bulk, accumulate at the brush-bulk interface, i.e., stay in proximity of the brush segments aligned parallel to the grafting surface. This creates an interesting situation, where the counterions are not completely within the brush layer, yet they fully screen the brush charges. Such “freer” conditions enable the counterions to achieve very high velocity, thereby ensuring that the water solvating the counterions themselves move very fast triggering the significantly augmented EOS transport. Probing deeper we can identify that the bending-tilting driven brush deformation, enforcing the brushes to align parallel to the substrate, results from the anti-electrophoretic behavior of the brushes, where despite being positively charged, the brushes move against the electric field direction. Such an anti-electrophoretic behavior of the PE brushes, which has not been reported before, can be associated with the very fast velocities of the negatively charged counterions and the electrostatic and hydrodynamic coupling of the counterions with the positive functional groups of the brushes. Here, we anticipate that the findings of this paper will shed light on strategies for nanochannel flow, the anti-electrophoretic response of charged polymer chains, and the significance of capturing the detailed chemical architecture of polyelectrolytes in nanoscale science and engineering.

• Research Organization: University of Maryland, College Park, MD (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0017741
• OSTI ID: 2568483
• Journal Information: ACS Applied Polymer Materials, Journal Name: ACS Applied Polymer Materials Journal Issue: 5 Vol. 7; ISSN 2637-6105
• Publisher: ACS Publications
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
counterions
electric fields
electroosmotic flow
electrophoresis
hydrodynamic interactions
interfaces
ions
nanochannel
polyelectrolyte brushes