All-Atom Molecular Dynamics Simulations of the Temperature Response of Densely Grafted Polyelectrolyte Brushes*

Polyelectrolytes (PEs) are large molecules formed by a combination of charged repeating units. PE chains can form a “brush”-like structure when end-grafted to a surface in close proximity of each other. Such PE brushes have been utilized in a wide variety of applications such as current rectification, drug delivery, colloidal stabilization, etc. due to their ability to respond to environmental factors such as pH, solvent quality, and temperature. We use all-atom Molecular Dynamics (MD) simulations to probe the effect of temperature on several structural and dynamical properties of water-swollen PE brushes such as the brush height, hydrogen bonding, counterion solvation structure, tetrahedral order parameter of the water molecules as well as the mobility of the brush-supported water and counterions. Our results indicate a reduced mass density of the trapped water molecules and an enhanced replacement of the counterion solvation water with PE functional groups at elevated temperatures, thereby promoting “water-in-salt”-like behaviour (with the counterions acting as the cations and the PE brush repeating units acting as the anions of the salt).