All-atom molecular dynamics simulations showing the dynamics of small organic molecules in water-solvated polyelectrolyte brush layers.

Polyelectrolyte brushes can introduce functionality to surfaces and because of this, these brushes have been studied extensively. In many applications, these brushes are used in solutions that contain a variety of molecules. While the interaction between polyelectrolyte brushes and molecules has been studied coarse-grained simulations and experiments, such interaction has not been studied in molecular detail.

All-atom molecular dynamics simulations of polymer and polyelectrolyte brushes.

Densely grafted polymer and polyelectrolyte (PE) brushes, owing to their significant abilities to functionalize surfaces for a plethora of applications in sensing, diagnostics, current rectification, surface wettability modification, drug delivery, and oil recovery, have attracted significant attention over the past several decades. Unfortunately, most of the attention has primarily focused on understanding the properties of the grafted polymer and the PE chains with little attention devoted to studying the behavior of the brush-supported ions (counterions needed to screen the PE chains) and water molecules. Over the past few years, our group has been at the forefront of addressing this gap: we have employed all-atom molecular dynamics (MD) simulations for studying a wide variety of polymer and PE brush systems with specific attention to unraveling the properties and behavior of the brush-supported water molecules and ions.

All-Atom Molecular Dynamics Simulations of Uncharged Linear Polymer Bottlebrushes: Effect of the Brush Sizes and the Number of Side-Chain Monomers.

Bottlebrush polymers (BBPs), characterized by grafted polymer side chains on linear backbone polymer chain, have emerged as a unique and versatile class of macromolecules with extensive applications in the fields of material science, electronics, battery materials, self-healing technology, etc. In this paper, we employ all-atom molecular dynamics (MD) simulations to present a comprehensive study of poly(methyl methacrylate)--poly(2-ethyl-2-oxazoline) (PMMA--PEtOx) BBP and its structural and hydration properties for varying number of backbone monomers () and side chain monomers (), as well as properties of water molecules supported by the BBP. We find that the radius of gyration follows a scaling of ∼ for smaller grafts and ∼ for longer grafts.

Hydrophilic and Apolar Hydration in Densely Grafted Cationic Brushes and Counterions with Large Mobilities.

We employ an all-atom molecular dynamics (MD) simulation framework to unravel water microstructure and ion properties for cationic [poly(2-(methacryloyloxy)ethyl) trimethylammonium chloride] (PMETAC) brushes with chloride ions as counterions. First, we identify locally separate water domains (or first hydration shells) each around {N(CH)} and the C═O functional groups of the PMETAC chain and one around the Cl ion. These first hydration shells around the respective moieties overlap, and the extent of the overlap depends on the nature of the species triggering it.

Interplay of Local Heating, Nanoconfinement, and Tunable Liquid-Wall Interactions Drive Rapid Imbibition and Pronounced Mixing Between Two Immiscible Liquids.

Designing novel and energy-efficient strategies for disturbing stable interfaces between two immiscible liquids hold the key for a myriad of applications. In this Letter, we propose a highly effective strategy where localized heating (costing less energy) of an interface between two immiscible liquids confined in a nanochannel enable rapid imbibition and mixing between these two liquids. The exact dynamics (imbibition or mixing) depend on the relative wettability of these two liquids to the nanochannel wall.