NSF-DFG Confine: MolPEC – Molecular Theory of Weak Polyelectrolytes in Confined Space

In this project supported by the Chemical Theory, Models and Computational Methods Program (CTMC) of the Division of Chemistry, Professor Jianzhong Wu of the University of California-Riverside is developing theoretical models that describe a class of polymers known as weak polyelectrolytes (WPEs). This is a collaborative project with researchers from the Georg-August-Universität Göttingen, Germany.

WPEs are a large class of macromolecules that may either protonate or deprotonate depending upon the environmental conditions such as pH and salt concentration. Their stimuli-responsive behavior has been broadly utilized in functional “smart” materials for applications such as targeted drug delivery or underwater adhesion. Whereas practical applications often entail chemical and physical processes under spatial confinement, the structure and dynamics of WPEs remain incompletely understood due to the strong coupling of reaction and polymer-mediated correlations at both monomer and polymer scales.

The rational design of WPE systems is calling for advances in theoretical and computational methods that are able to accurately describe confinement effects on local solution environment, protonation/deprotonation equilibrium, and the dynamics of polymers reacting with ionizable surfaces. This research aims to develop a theoretical framework for describing the properties of WPEs in confined space and their responses to environmental conditions including solution pH, electrolyte composition, and the chemistry of confinement.

We will utilize these techniques to investigate the interplay between ionic size, valence, ionization, surface reactions and the dynamics of polymer binding that cannot be reliably addressed with conventional methods. The theoretical and computational advances will contribute to a rational design of weak polyelectrolyte systems for a wide spectrum of technological applications.

Building on complementary advances in polymer density functional theory (PDFT) and molecular simulation, the US-German team will study the structure, thermodynamics, and dynamics of weak polyelectrolytes at and between surfaces. The idea is to combine and extend Ising Density Functional Theory (iDFT) and Single-Chain-in-Mean-Field (SCMF) simulation. iDFT considers single-chain configurations and ionization states of segments on equal footing and captures liquid-like packing and electrostatic correlations via the molecular density.

The joint probability distribution of configurations and ionization states of an entire macromolecule is dictated by a single-chain potential, which, in turn, is a functional of the molecular density. The high-dimensional molecular density will be efficiently evaluated via SCMF simulation on parallel, GPU-accelerated supercomputers, employing the iDFT single-chain potential.

The team will extend the simulation code, SOft coarse-grained Monte-carlo Acceleration (SOMA), to incorporate electrostatic interactions and nonlocal interactions along the molecular contour. The particle-based simulation, Dynamic-iDFT (D-iDFT), accounts for long-range fluctuations and allows us to study the configuration dynamics. Additionally, we will derive a segment-based dynamic iDFT (SD-iDFT) for describing the local polymer mass and charge density in response to environmental changes.

The generic nature of the theoretical techniques proposed in this work ensures broad applications to diverse phenomena in polymeric and biological systems. This project will provide training opportunities for early career scientists to gain interdisciplinary research experience and cultivate their career interests in computational molecular engineering.

In addition to supporting graduate students, it offers research-based thesis projects for undergrads in active military service, veterans, and students from the University Honors Program (UHP). This project is being awarded through the “Chemistry and Transport in Confined Spaces (NSF-DFG Confine)" opportunity, a collaborative solicitation that involves the National Science Foundation and Deutsche Forschungsgemeinschaft (DFG).

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.