Atomistics Explorations of Fundamental Features of Cationic Polyelectrolyte Brushes through Molecular Simulations and Machine learning.
ORAL
Abstract
Densely grafted cationic brushes have significant applications in areas such as water filtration, drug delivery, and antimicrobial surface creation. Gaining a deeper understanding of the microscopic properties of these systems is essential for explaining their macroscopic behavior and optimizing their performance in these applications. In this study, we employ all-atom molecular dynamics (MD) simulations and machine learning (ML) techniques to explore the water microstructure, ion dynamics, and hydration behavior of a very commonly used cationic brush, poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC). First, we investigate the hydration shells and ion behavior within the PMETAC brush system, identifying that the {N(CH3)3}+ and C═O groups respectively demonstrates apolar and hydrophillic hydration. Also the Cl- counterion has high mobility inside PMETAC brushes due to the mismatch of hydration strength of {N(CH3)3}+ and Cl-. Next, we introduce an unsupervised machine learning framework to identify two hydration states around the {N(CH3)3}+ group, showing that increased brush grafting density leads to a shift towards less structured water molecules. Last, we extend our simulations to study the impact of different halide counterions (I–, Br–, Cl–, and F–) on brush behavior, revealing trends in ion binding and brush compression due to chaotropic effects, with water structuring and halide mobility varying based on the ion's charge density. This combined ML-MD approach offers valuable insights into the role of hydration in soft matter systems and highlights the complex interplay between polyelectrolytes, water, and ions.
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Publication: 1) R. Ishraaq, T. S. Akash, A. K. Bera and S. Das, Hydrophilic and Apolar Hydration in Densely Grafted Cationic Brushes and Counterions with Large Mobilities, J. Phys. Chem. B, 2023, 128(1), 381–392. (accepted)<br>2 ) R. Ishraaq and S. Das, All-Atom Molecular Dynamics Simulations of Cationic Polyelectrolyte Brushes in the Presence of Halide Counterions, Macromolecules, 2024, 57(7), 3037–3046. (accepted)<br>3) R. Ishraaq, T. S. Akash and S. Das, Combined Machine Learning and Molecular Dynamics Reveal Two States of Hydration of a Single Functional Group of Cationic Polymeric Brushes, Macromolecules, 2024, 57, 5300–5312. (accepted)<br>4) R. Ishraaq and S. Das, All-atom molecular dynamics simulations of polymer and polyelectrolyte brushes, Chemical Communication, 2024, 60, 6093–6129. (accepted)
