NSF-DFG Confine: MolPEC -- Molecular theory of weak polyelectrolytes in confined space

基于聚合物密度泛函理论（PDFT）和分子模拟的互补进展，美德团队将研究表面和表面之间的弱聚电解质的结构、热力学和动力学。其思想是结合和扩展伊辛密度泛函理论（iDFT）和单链平均场（SCMF）模拟。iDFT考虑单链构型和相等基础上的片段电离状态，并通过分子密度ρ(X)捕获液体样填料和静电相关性。整个大分子的构型和电离态的联合概率分布是由单链电位ω(X)决定的，而ω(X)又是分子密度的函数。利用iDFT单链势，在并行、gpu加速的超级计算机上进行SCMF模拟，有效地评估了高维分子密度。我们将扩展模拟代码SOft粗粒度蒙特卡罗加速（SOMA），以结合静电相互作用和沿分子轮廓的非局部相互作用。基于粒子的模拟，动态idft (D-iDFT)，考虑了长期波动，使我们能够研究结构动力学。此外，我们将推导出基于段的动态iDFT (SD-iDFT)，用于描述响应环境变化的局部聚合物质量和电荷密度。联合计算方案将应用于四个典型的科学问题：(i) SCMF/iDFT模拟将研究弱聚电解质在表面上的吸附，重点关注单链构型、电离态和聚合物表面相互作用之间的耦合。（ii）此外，iDFT将研究表面自由能和聚合物诱导的表面之间的相互作用，并研究片段序列和表面非均质性的作用。（iii）随后，我们将研究聚阳离子和聚阴离子在受限水溶液中的聚集，重点研究薄膜中的润湿和相行为以及几何约束之间的相互作用。（iv）此外，我们将使用D-iDFT模拟和SD-iDFT来研究受限制的弱聚电解质对环境条件（如pH或盐浓度）变化的响应集体动力学。这些分子模拟能够从聚合物电离和单链构型的潜在动力学中预测片段和电荷密度分布的时间演变。在所有情况下，我们将研究模型系统，通过比较SCMF模拟、iDFT和文献数据来验证我们的计算，并随后将我们的研究扩展到更复杂的系统，考虑不同的片段序列和约束的化学性质。这些理论和计算的进步将有助于弱聚电解质系统的合理设计，用于广泛的技术应用。

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, ρ(X). This joint probability distribution of configurations and ionization states of an entire macromolecule is dictated by a single-chain potential, ω(X), 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. We 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 combined computational scheme will be applied to four prototypical, scientific questions: (i) SCMF/iDFT simulations will study the adsorption of weak polyelectrolytes onto surfaces, focusing on the coupling between single-chain configurations, ionization states, and polymer-surface interactions. (ii) Additionally, iDFT will investigate surface free energies and polymer-induced interactions between surfaces, and study the role of segment sequences and surface heterogeneities. (iii) Subsequently, we will study the coacervation of polycations and polyanions in confined aqueous solution, focusing on the interplay between wetting and phase behavior in thin films and geometric confinement. (iv) Moreover, we will use D-iDFT simulations and SD-iDFT to study the collective dynamics of confined, weak polyelectrolytes in response to changes of environmental conditions, such as pH or salt concentration. These molecular simulations are able to predict the temporal evolution of segment and charge density profiles from the underlying dynamics of polymer ionization and single-chain configurations. In all cases we will study model systems to validate our computations by comparison between SCMF simulation, iDFT, and literature data, and subsequently extend our studies to more complex systems, accounting for different segment sequences and chemistry of the confinement. These theoretical and computational advances will contribute to a rational design of weak polyelectrolyte systems for a wide spectrum of technological applications.