Polyelectrolyte Phase Behavior and Transport

非技术总结：带电聚合物，称为聚电解质，在生物学中很常见，包括DNA，RNA，蛋白质和粘液层。 它们越来越多地用于从药物输送到传感膜或电池的应用。 用于这些应用的聚电解质膜可以通过将表面依次浸入带负电荷的电解质中，然后浸入带正电荷的电解质中，逐层构建。 另外，用水溶胀的凝胶，称为“凝聚层”，可以通过混合两种带相反电荷的聚电解质来制备。 尽管这些材料在生物学和高级应用中的重要性，但它们的行为知之甚少，目前既不了解凝聚层的性质，也不了解逐层膜的生长速率。虽然最近已经开发出了有前途的理论，但很少有系统的实验数据来测试和证实这些理论，以帮助设计先进的材料。 为了提供这种测试，本项目将使用简单和先进的实验方法来测量凝聚层的组成，以及逐层膜的生长速率和厚度。 这些测量将在不同的盐浓度和pH值下系统地进行，以建立测试和确认新开发理论所需的定量趋势，并为设计由聚电解质制成的先进材料提供坚实的基础。 这些知识也与生物系统有关，包括带正电荷的蛋白质与带负电荷的DNA的相互作用，后者控制染色体的结构和功能。 除了研究，本项目的更广泛的影响将包括研究生和本科生的教育，推广，以及与此主题相关的专门计算代码的开发。技术概要：为了理解和测试带相反电荷的聚电解质组件的平衡和动力学理论，将进行几个阶段的研究。首先，相行为，包括在凝聚层和上清液相的四个常见的聚乙烯混合物的个别聚离子的组合物将通过高压液相色谱法，质子NMR，和其他方法进行测量。结果将与新理论的预测进行比较，并用于测试和改进这些理论。用酸和碱滴定将用于确定离子配对平衡常数、电离平衡和热力学“chi”参数。此外，这些聚电解质的逐层（LBL）生长速率将被测量，由理论和相行为确定的热力学信息将被用来预测这些生长速率。 聚离子的扩散系数，通过多层膜的预测LBL的增长将推断从原子分子动力学（MD）模拟的聚阴离子和聚阳离子在水和盐的离子配对的强度。

NON-TECHNICAL SUMMARY:Electrically charged polymers, called polyelectrolytes, are common in biology and include DNA, RNA, proteins, and mucous layers. They are increasingly used for applications ranging from drug delivery to membranes for sensing or batteries. Membranes of polyelectrolytes for these applications can be built up, layer by layer, by sequentially dipping a surface into a negatively charged polyelectrolyte followed by dipping into a positively charged one. Additionally, gels swollen with water, known as "coacervates", can be made by mixing two oppositely charged polyelectrolytes. Despite the importance of these materials in biology and advanced applications, their behavior is poorly known, and neither the properties of coacervates nor the rate of growth of layer-by-layer membranes is understood at present. While promising theories for such polyelectrolyte materials have recently been developed, there is little systematic experimental data to test and confirm these theories so as to help design advanced materials. To provide such tests, this project will use both simple and advanced experimental methods to measure the composition of coacervates, and the growth rate and thickness of layer-by-layer films. These measurements will be carried out systematically with varying salt concentration and pH to establish quantitative trends needed to test and confirm newly developed theory and provide a firm base for design of advanced materials made from polyelectrolytes. Such knowledge is also relevant in biological systems, including the interactions of positively charged proteins with negatively charged DNA, which controls the structure and function of chromosomes. Beyond the research, broader impacts of this project will include the education of graduate and undergraduate students, outreach, and development of specialized computational codes relevant to this topic.TECHNICAL SUMMARY:To understand and test theories for the equilibrium and dynamics of assemblies of oppositely charged polyelectrolytes, several phases of study will be performed. First, the phase behavior including compositions of individual polyions in both coacervate and supernatant phases for four common polyelectrolyte mixtures will be measured by high pressure liquid chromatography, proton NMR, and other methods. The results will be compared to the predictions of new theories, and used to test and improve these theories. Titrations with acid and base will be used to determine ion pairing equilibrium constants, ionization equilibrium, and thermodynamic "chi" parameters. In addition, Layer-by-Layer (LbL) growth rates for these polyelectrolytes will be measured and the thermodynamic information determined by theory and phase behavior will be used to predict these growth rates. The diffusivities of polyions through the polyelectrolyte multilayer needed for predictions of LbL growth will be inferred from strengths of ion pairing obtained from atomistic molecular dynamics (MD) simulations of a polyanion and polycation in water and salt.