Charge-Density-Specific Response of Grafted Polyelectrolytes to Electric Fields: Bending or Tilting?

TH Pial and M Prajapati and BS Chava and HS Sachar and S Das, MACROMOLECULES, 55, 2413-2423 (2022).

DOI: 10.1021/acs.macromol.2c00237

The response of polyelectrolytes (PEs) to applied electric fields drives applications in energetics, diagnostics, materials development, and many more. Here we employ all-atom molecular dynamics (MD) simulations to probe the responseof grafted PE brushes to axial electricfields. For PEs with largecharge densities, the electricfield triggers a left-right asymmetricdistribution of counterions around the PE backbone: consequently,depending on the location (left or right), there is an unequalscreening and an unequal force on the PE functional groupscausing a bending-driven brush height reduction. However, for theweakly charged PEs, the electricfield causes a uniform distributionof the counterions across the brush, enforcing a uniform (without left-right asymmetry) partially unscreened PE brush: therefore, allthe brush segments experience similar force causing a brush tilting-driven brush height reduction. Such bending versus tilting responses is commensurate with the electric-field-driven increase (decrease) in the flexibility of strongly (weakly) charged PEs

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