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

在聚合物密度泛函理论(PDFT)和分子模拟的互补进展的基础上，美国和德国的团队将研究表面和表面之间弱聚电解质的结构、热力学和动力学。我们的想法是结合和扩展伊辛密度泛函理论(IDFT)和平均场单链(SCMF)模拟。IDFT考虑了链段的单链构型和电离态，并通过分子密度ρ(X)捕捉了液体状堆积和静电关联。整个大分子的构型和电离态的这种联合概率分布由单链势ω(X)决定，而单链势又是分子密度的泛函。在GPU加速的并行超级计算机上，利用iDFT单链势，通过SCMF模拟，将有效地评估高维分子密度。我们将扩展模拟代码，软粗颗粒蒙特卡罗加速(SOMA)，以包括分子轮廓上的静电相互作用和非局部相互作用。基于粒子的动态离散傅立叶变换(D-IDFT)考虑了长程波动，使我们能够研究构型动力学。此外，我们将导出一个基于分段的动态密度分布傅立叶变换(SD-IDFT)来描述局部聚合物质量和电荷密度对环境变化的响应。组合的计算方案将被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，并研究链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凝聚，重点是薄膜中的润湿和相行为与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、弱聚电解质的集体动力学响应环境条件的变化，例如pH或盐浓度。这些分子模拟能够根据聚合物电离和单链构型的基本动力学来预测链段和电荷密度分布的时间演变。在所有情况下，我们都将研究模型系统，通过SCMF模拟、iDFT和文献数据的比较来验证我们的计算，并随后将我们的研究扩展到更复杂的系统，考虑到不同的分段顺序和约束化学。这些理论和计算方面的进展将有助于合理设计适用于广泛技术应用的弱聚电解质体系。

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.