Interfacial Microstructure of Neutral and Charged Polymer Brushes: A Density Functional Theory Study

Polymer density functional theory (PDFT) is a computationally efficient and popular statistical mechanics theory of complex fluids for capturing the interfacial microstructure of grafted polymer brushes (PBs). Undoubtedly, the intramolecular and intermolecular interactions in PDFT (e.g., excluded volume interactions and electrostatic interactions) are affected by the grafting behaviors. However, how to treat these interactions coupled with the physical constraints of end-grafted PBs remains unclear in the literature. Even worse, there are remarkable differences in the density profiles of PBs between the predictions from PDFT and simulations. Herein, we propose a PDFT for studying neutral and charged grafted PBs, and provide its rigorous derivation and numerical details. This PDFT is successfully validated, where the density distributions of neutral and weakly charged PBs predicted by the PDFT are in excellent agreement with the results from Monte Carlo (MC) and molecular dynamics (MD) simulations. This work provides a powerful and accurate theoretical method to reveal the interfacial microstructure of grafted PBs.