1. Polyelectrolyte Adsorption at a Conducting Interface: A Simulation Study Paul R. Van Tassel Dept. of Chemical & Environmental Engineering, Yale University
Continuous polyelectrolyte adsorption under an applied potential – where saturation is suppressed and film growth can continue up to hundreds of nanometers – offers great opportunities (single component polyelectrolyte films of controlled mass realized in a single step), but raises fundamental questions. Molecular simulation is used here to gain mechanistic and predictive insight into this promising yet curious phenomenon.
Interaction free energy per Bjerrum length lB (lB = 0.7 nm for an aqueous solvent at 298 K) versus center-to-center separation of two polyelectrolytes, modeled as rigid cylinders of linear charge density 8e/lB (e = elementary charge), parallel to one another, in the presence of counter-ions of charge -2e, for various counter-ion diameters, as determined by Monte Carlo simulation. .
Simulation snapshots of two interacting polyelectrolytes (green) in the presence of divalent counter-ions (red) of diameter = 0.5 lB, at various polymer-polymer separations (lB = 0.7 nm). As the separation decreases, the counter-ions initially arrange preferentially between the polymers (resulting in net attraction), but eventually are squeezed out of this space (resulting in repulsion).