Charge-Density-Specific Response of Grafted Polyelectrolytes to Electric Fields: Bending or Tilting?
Turash Haque Pial, Mihir Prajapati, Bhargav Sai Chava, Harnoor Singh Sachar, Siddhartha Das
Abstract
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 response of grafted PE brushes to axial electric fields. For PEs with large charge densities, the electric field triggers a left–right asymmetric distribution of counterions around the PE backbone: consequently, depending on the location (left or right), there is an unequal screening and an unequal force on the PE functional groups causing a bending-driven brush height reduction. However, for the weakly charged PEs, the electric field causes a uniform distribution of the counterions across the brush, enforcing a uniform (without left–right asymmetry) partially unscreened PE brush: therefore, all the 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.